Court Opinion

ID: 4119506
Source: CourtListenerOpinion
Date Created: 2017-01-27 22:40:32.697097+00
Date Added: 2024-06-11T14:46:47.550904
License: Public Domain

The President’s Constitutional Authority to Conduct
                        Military Operations Against Terrorists and
                                 Nations Supporting Them
         The President has broad constitutional power to take military action in response to the terrorist attacks
           on the United States on September 11, 2001. Congress has acknowledged this inherent executive
           power in both the War Powers Resolution and the Joint Resolution passed by Congress on Septem-
           ber 14, 2001.
         The President has constitutional power not only to retaliate against any person, organization, or state
           suspected of involvement in terrorist attacks on the United States, but also against foreign states
           suspected of harboring or supporting such organizations.
         The President may deploy military force preemptively against terrorist organizations or the states that
           harbor or support them, whether or not they can be linked to the specific terrorist incidents of
           September 11.

                                                                                           September 25, 2001

                 MEMORANDUM OPINION FOR THE DEPUTY COUNSEL TO THE PRESIDENT *

             You have asked for our opinion as to the scope of the President’s authority to
         take military action in response to the terrorist attacks on the United States on
         September 11, 2001. We conclude that the President has broad constitutional
         power to use military force. Congress has acknowledged this inherent executive
         power in both the War Powers Resolution, Pub. L. No. 93-148, 87 Stat. 555
         (1973), codified at 50 U.S.C. §§ 1541-1548 (the “WPR”), and in the Joint
         Resolution passed by Congress on September 14, 2001, Pub. L. No. 107-40, 115
         Stat. 224 (2001). Further, the President has the constitutional power not only to
         retaliate against any person, organization, or state suspected of involvement in
         terrorist attacks on the United States, but also against foreign states suspected of
         harboring or supporting such organizations. Finally, the President may deploy
         military force preemptively against terrorist organizations or the states that harbor
         or support them, whether or not they can be linked to the specific terrorist
         incidents of September 11.
             Our analysis falls into four parts. First, we examine the Constitution’s text and
         structure. We conclude that the Constitution vests the President with the plenary
         authority, as Commander in Chief and the sole organ of the Nation in its foreign
         relations, to use military force abroad—especially in response to grave national
         emergencies created by sudden, unforeseen attacks on the people and territory of
         the United States. Second, we confirm that conclusion by reviewing the executive
         and judicial statements and decisions interpreting the Constitution and the

            *
              Editor’s Note: For the book edition of this memorandum opinion, some of the internet citations
         have been updated or replaced with citations of equivalent printed authorities.

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             President’s powers under it. Third, we analyze the relevant practice of the United
             States, including recent history, that supports the view that the President has the
             authority to deploy military force in response to emergency conditions such as
             those created by the September 11, 2001 terrorist attacks. Finally, we discuss
             congressional enactments that, in our view, acknowledge the President’s plenary
             authority to use force to respond to the terrorist attack on the United States.
                Our review establishes that all three branches of the federal government—
             Congress, the Executive, and the Judiciary—agree that the President has broad
             authority to use military force abroad, including the ability to deter future attacks.

                                                               I.

                The President’s constitutional power to defend the United States and the lives
             of its people must be understood in light of the Founders’ express intention to
             create a federal government “cloathed with all the powers requisite to [the]
             complete execution of its trust.” The Federalist No. 23, at 122 (Alexander
             Hamilton) (Charles R. Kesler ed., 1999). Foremost among the objectives commit-
             ted to that trust by the Constitution is the security of the Nation. 1 As Hamilton
             explained in arguing for the Constitution’s adoption, because “the circumstances
             which may affect the public safety are [not] reducible within certain determinate
             limits, . . . it must be admitted, as a necessary consequence that there can be no
             limitation of that authority which is to provide for the defense and protection of
             the community in any matter essential to its efficiency.” Id. 2
                “It is ‘obvious and unarguable’ that no governmental interest is more compel-
             ling than the security of the Nation.” Haig v. Agee, 453 U.S. 280, 307 (1981)

                 1
                   “As Lincoln aptly said, ‘[is] it possible to lose the nation and yet preserve the Constitution?’”
             Youngstown Sheet & Tube Co. v. Sawyer, 343 U.S. 579, 662 (1952) (Clark, J., concurring in judgment).
                 2
                   See also The Federalist No. 34, at 207 (Alexander Hamilton) (Clinton Rossiter ed., 1961) (federal
             government is to possess “an indefinite power of providing for emergencies as they might arise”); id.
             No. 41, at 256 (James Madison) (“Security against foreign danger is one of the primitive objects of
             civil society. . . . The powers requisite for attaining it must be effectually confided to the federal
             councils.”). Many Supreme Court opinions echo Hamilton’s argument that the Constitution presuppos-
             es the indefinite and unpredictable nature of the “the circumstances which may affect the public
             safety,” and that the federal government’s powers are correspondingly broad. See, e.g., Dames &
             Moore v. Regan, 453 U.S. 654, 662 (1981) (noting that the President “exercis[es] the executive
             authority in a world that presents each day some new challenge with which he must deal”); Hamilton v.
             Regents, 293 U.S. 245, 264 (1934) (federal government’s war powers are “well-nigh limitless” in
             extent); Stewart v. Kahn, 78 U.S. (11 Wall.) 493, 506 (1870) (“The measures to be taken in carrying on
             war . . . are not defined [in the Constitution]. The decision of all such questions rests wholly in the
             discretion of those to whom the substantial powers involved are confided by the Constitution.”); Miller
             v. United States, 78 U.S. (11 Wall.) 268, 305 (1870) (“The Constitution confers upon Congress
             expressly power to declare war, grant letters of marque and reprisal, and make rules respecting captures
             on land and water. Upon the exercise of these powers no restrictions are imposed. Of course the power
             to declare war involves the power to prosecute it by all means and in any manner in which war may be
             legitimately prosecuted.”).

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         (citation omitted). Within the limits that the Constitution itself imposes, the scope
         and distribution of the powers to protect national security must be construed to
         authorize the most efficacious defense of the Nation and its interests in accordance
         “with the realistic purposes of the entire instrument.” Lichter v. United States, 334
         U.S. 742, 782 (1948). Nor is the authority to protect national security limited to
         actions necessary for “victories in the field.” Application of Yamashita, 327 U.S. 1,
         12 (1946). The authority over national security “carries with it the inherent power
         to guard against the immediate renewal of the conflict.” Id.
             We now turn to the more precise question of the President’s inherent constitu-
         tional powers to use military force.
             Constitutional Text. The text, structure and history of the Constitution establish
         that the Founders entrusted the President with the primary responsibility, and
         therefore the power, to use military force in situations of emergency. Article II,
         Section 2 states that the “President shall be Commander in Chief of the Army and
         Navy of the United States, and of the Militia of the several States, when called into
         the actual Service of the United States.” U.S. Const. art. II, § 2, cl. 1. He is further
         vested with all of “the executive Power” and the duty to execute the laws. U.S.
         Const. art. II, § 1. These powers give the President broad constitutional authority
         to use military force in response to threats to the national security and foreign
         policy of the United States. 3 During the period leading up to the Constitution’s
         ratification, the power to initiate hostilities and to control the escalation of conflict
         had been long understood to rest in the hands of the Executive Branch. 4
             By their terms, these provisions vest full control of the military forces of the
         United States in the President. The power of the President is at its zenith under the
         Constitution when the President is directing military operations of the armed
         forces, because the power of Commander in Chief is assigned solely to the
         President. It has long been the view of this Office that the Commander-in-Chief
         Clause is a substantive grant of authority to the President and that the scope of the
         President’s authority to commit the armed forces to combat is very broad. See,
         e.g., Memorandum for Charles W. Colson, Special Counsel to the President, from

             3
               See Johnson v. Eisentrager, 339 U.S. 763, 789 (1950) (President has authority to deploy United
         States armed forces “abroad or to any particular region”); Fleming v. Page, 50 U.S. (9 How.) 603, 615
         (1850) (“As commander-in-chief, [the President] is authorized to direct the movements of the naval and
         military forces placed by law at his command, and to employ them in the manner he may deem most
         effectual . . . .”); Loving v. United States, 517 U.S. 748, 776 (1996) (Scalia, J., concurring in part and
         concurring in judgment) (The “inherent powers” of the Commander in Chief “are clearly extensive.”);
         Maul v. United States, 274 U.S. 501, 515-16 (1927) (Brandeis & Holmes, JJ., concurring) (President
         “may direct any revenue cutter to cruise in any waters in order to perform any duty of the service”);
         Massachusetts v. Laird, 451 F.2d 26, 32 (1st Cir. 1971) (the President has “power as Commander-in-
         Chief to station forces abroad”); Authority to Use United States Military Forces in Somalia, 16 Op.
         O.L.C. 6 (1992).
             4
               See John C. Yoo, The Continuation of Politics by Other Means: The Original Understanding of
         War Powers, 84 Cal. L. Rev. 167, 196-241 (1996).

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             William H. Rehnquist, Assistant Attorney General, Office of Legal Counsel, Re:
             The President and the War Power: South Vietnam and the Cambodian Sanctuaries
             (May 22, 1970) (the “Rehnquist Memo”). The President’s complete discretion in
             exercising the Commander-in-Chief power has also been recognized by the courts.
             In the Prize Cases, 67 U.S. (2 Black) 635, 670 (1862), for example, the Court
             explained that, whether the President “in fulfilling his duties as Commander in-
             Chief” had met with a situation justifying treating the southern States as belliger-
             ents and instituting a blockade, was a question “to be decided by him” and which
             the Court could not question, but must leave to “the political department of the
             Government to which this power was entrusted.” 5
                Some commentators have read the constitutional text differently. They argue
             that the vesting of the power to declare war gives Congress the sole authority to
             decide whether to make war. 6 This view misreads the constitutional text and

                  5
                    See Prize Cases, 67 U.S. at 670 (“He must determine what degree of force the crisis demands.”);
             see also Eisentrager, 339 U.S. at 789 (“Certainly it is not the function of the Judiciary to entertain
             private litigation—even by a citizen—which challenges the legality, the wisdom, or the propriety of the
             Commander-in-Chief in sending our armed forces abroad or to any particular region.”); Chicago &
             Southern Air Lines v. Waterman Steamship Corp., 333 U.S. 103, 111 (1948) (“The President, both as
             Commander-in-Chief and as the Nation’s organ for foreign affairs, has available intelligence services
             whose reports are not and ought not to be published to the world. It would be intolerable that courts,
             without the relevant information, should review and perhaps nullify actions of the Executive taken on
             information properly held secret.”); Ramirez de Arellano v. Weinberger, 745 F.2d 1500, 1561 (D.C.
             Cir. 1984) (Scalia, J., dissenting), vacated by 471 U.S. 1113 (1985); Ex parte Vallandigham, 28 F. Cas.
             874, 922 (C.C.S.D. Ohio 1863) (No. 16,816) (in acting “under this power where there is no express
             legislative declaration, the president is guided solely by his own judgment and discretion”);
             Hefleblower v. United States, 21 Ct. Cl. 228, 238 (Ct. Cl. 1886) (“The responsibility of declaring what
             portions of the country were in insurrection and of declaring when the insurrection came to an end was
             accorded to the President; when he declared a portion of the country to be in insurrection the judiciary
             cannot try the issue and find the territory national; conversely, when the President declared the
             insurrection at an end in any portion of the country, the judiciary cannot try the issue and find the
             territory hostile.”); cf. United States v. Chemical Found., Inc., 272 U.S. 1, 12 (1926) (“It was peculiarly
             within the province of the Commander-in-Chief to know the facts and to determine what disposition
             should be made of enemy properties in order effectively to carry on the war.”).
                  6
                    See, e.g., Louis Fisher, Presidential War Power 185-206 (1995); John Hart Ely, War and Respon-
             sibility: Constitutional Lessons of Vietnam and Its Aftermath 3-5 (1993); Michael J. Glennon,
             Constitutional Diplomacy 80-84 (1990); Louis Henkin, Constitutionalism, Democracy, and Foreign
             Affairs 109 (1990); Harold Hongju Koh, The National Security Constitution: Sharing Power After the
             Iran-Contra Affair 158-61 (1990); Francis D. Wormuth & Edwin B. Firmage, To Chain the Dog of
             War: The War Power of Congress in History and Law (2d ed. 1989).
                  Other scholars, however, have argued that the President has the constitutional authority to initiate
             military hostilities without prior congressional authorization. See, e.g., Edward S. Corwin, The
             President: Office and Powers 1787-1984 (5th ed. 1984); Philip Bobbitt, War Powers: An Essay on
             John Hart Ely’s “War and Responsibility: Constitutional Lessons of Vietnam and Its Aftermath,” 92
             Mich. L. Rev. 1364 (1994); Robert H. Bork, Erosion of the President’s Power in Foreign Affairs, 68
             Wash. U.L.Q. 693 (1990); Henry P. Monaghan, Presidential War-Making, 50 B.U.L. Rev. 19 (1970);
             W. Michael Reisman, Some Lessons from Iraq: International Law and Democratic Politics, 16 Yale J.
             Int’l L. 203 (1991); Eugene V. Rostow, “Once More unto the Breach”: The War Powers Resolution

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         misunderstands the nature of a declaration of war. Declaring war is not tantamount
         to making war—indeed, the Constitutional Convention specifically amended the
         working draft of the Constitution that had given Congress the power to make war.
         An earlier draft of the Constitution had given to Congress the power to “make”
         war. When it took up this clause on August 17, 1787, the Convention voted to
         change the clause from “make” to “declare.” 2 The Records of the Federal
         Convention of 1787, at 318-19 (Max Farrand ed., rev. ed. 1966). A supporter of
         the change argued that it would “leav[e] to the Executive the power to repel
         sudden attacks.” Id. at 318. Further, other elements of the Constitution describe
         “engaging” in war, which demonstrates that the Framers understood making and
         engaging in war to be broader than simply “declaring” war. See U.S. Const. art. I,
         § 10, cl. 3 (“No State shall, without the Consent of Congress . . . engage in War,
         unless actually invaded, or in such imminent Danger as will not admit of delay.”).
         A state constitution at the time of the ratification included provisions that prohibit-
         ed the governor from “making” war without legislative approval, S.C. Const. art.
         XXVI (1776), reprinted in 6 The Federal and State Constitutions 3247 (Francis
         Newton Thorpe ed., 1909). 7 If the Framers had wanted to require congressional
         consent before the initiation of military hostilities, they knew how to write such
         provisions.
            Finally, the Framing generation well understood that declarations of war were
         obsolete. Not all forms of hostilities rose to the level of a declared war: during the
         seventeenth and eighteenth centuries, Great Britain and colonial America waged
         numerous conflicts against other states without an official declaration of war. 8 As
         Alexander Hamilton observed during the ratification, “the ceremony of a formal
         denunciation of war has of late fallen into disuse.” The Federalist No. 25, at 165
         (Alexander Hamilton) (Clinton Rossiter ed., 1961). Instead of serving as an
         authorization to begin hostilities, a declaration of war was only necessary to
         “perfect” a conflict under international law. A declaration served to fully trans-
         form the international legal relationship between two states from one of peace to
         one of war. See 1 William Blackstone, Commentaries *249-50. Given this context,

         Revisited, 21 Val. U. L. Rev. 1 (1986); John C. Yoo, Kosovo, War Powers, and the Multilateral Future,
         148 U. Pa. L. Rev. 1673 (2000); Yoo, 84 Cal. L. Rev. 167.
             7
               A subsequent version made clear “that the governor and commander-in-chief shall have no power
         to commence war, or conclude peace, or enter into any final treaty” without legislative approval. S.C.
         Const. art. XXXIII (1778), reprinted in 6 The Federal and State Constitutions 3255 (Francis Newton
         Thorpe ed., 1909).
             8
               Of the eight major wars fought by Great Britain prior to the ratification of the Constitution, war
         was declared only once before the start of hostilities. See Yoo, 84 Cal. L. Rev. at 214-15. See also
         W. Taylor Reveley, III, War Powers of the President and Congress: Who Holds the Arrows and Olive
         Branch? 55 (1981) (“[U]ndeclared war was the norm in eighteenth-century European practice, a reality
         brought home to Americans when Britain’s Seven Years’ War with France began on this continent.”);
         William Michael Treanor, Fame, The Founding, and The Power to Declare War, 82 Cornell L. Rev.
         695, 709 (1997).

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             it is clear that Congress’s power to declare war does not constrain the President’s
             independent and plenary constitutional authority over the use of military force.
                 Constitutional Structure. Our reading of the text is reinforced by analysis of the
             constitutional structure. First, it is clear that the Constitution secures all federal
             executive power in the President to ensure a unity in purpose and energy in action.
             “Decision, activity, secrecy, and dispatch will generally characterize the proceed-
             ings of one man in a much more eminent degree than the proceedings of any
             greater number.” The Federalist No. 70, at 424 (Alexander Hamilton) (Clinton
             Rossiter ed., 1961). The centralization of authority in the President alone is
             particularly crucial in matters of national defense, war, and foreign policy, where a
             unitary executive can evaluate threats, consider policy choices, and mobilize
             national resources with a speed and energy that is far superior to any other branch.
             As Hamilton noted, “Energy in the executive is a leading character in the defini-
             tion of good government. It is essential to the protection of the community against
             foreign attacks.” Id. at 423. This is no less true in war. “Of all the cares or
             concerns of government, the direction of war most peculiarly demands those
             qualities which distinguish the exercise of power by a single hand.” Id. No. 74, at
             447 (Alexander Hamilton). 9
                 Second, the Constitution makes clear that the process used for conducting
             military hostilities is different from other government decisionmaking. In the area
             of domestic legislation, the Constitution creates a detailed, finely wrought
             procedure in which Congress plays the central role. In foreign affairs, however, the
             Constitution does not establish a mandatory, detailed, Congress-driven procedure
             for taking action. Rather, the Constitution vests the two branches with different
             powers—the President as Commander in Chief, Congress with control over
             funding and declaring war—without requiring that they follow a specific process
             in making war. By establishing this framework, the Framers expected that the
             process for warmaking would be far more flexible, and capable of quicker, more
             decisive action, than the legislative process. Thus, the President may use his
             Commander-in-Chief and executive powers to use military force to protect the
             Nation, subject to congressional appropriations and control over domestic
             legislation.

                 9
                   James Iredell (later an Associate Justice of the Supreme Court) argued in the North Carolina
             Ratifying Convention that “[f]rom the nature of the thing, the command of armies ought to be delegated
             to one person only. The secrecy, despatch, and decision, which are necessary in military operations, can
             only be expected from one person.” Debate in the North Carolina Ratifying Convention, in 4 Jonathan
             Elliott, The Debates in the Several State Conventions on the Adoption of the Federal Constitution as
             Recommended by the General Convention at Philadelphia in 1787, at 107 (2d ed. 1987). See also
             3 Joseph Story, Commentaries on the Constitution of the United States § 1485 (1833) (“Story”) (in
             military matters, “[u]nity of plan, promptitude, activity, and decision, are indispensable to success; and
             these can scarcely exist, except when a single magistrate is entrusted exclusively with the power”).

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             Third, the constitutional structure requires that any ambiguities in the allocation
         of a power that is executive in nature—such as the power to conduct military
         hostilities—must be resolved in favor of the Executive Branch. Article II, Section
         1 provides that “[t]he executive Power shall be vested in a President of the United
         States.” U.S. Const. art. II, § 1. By contrast, Article I’s Vesting Clause gives
         Congress only the powers “herein granted.” Id. art. I, § 1. This difference in
         language indicates that Congress’s legislative powers are limited to the list
         enumerated in Article I, Section 8, while the President’s powers include inherent
         executive powers that are unenumerated in the Constitution. To be sure, Article II
         lists specifically enumerated powers in addition to the Vesting Clause, and some
         have argued that this limits the “executive Power” granted in the Vesting Clause to
         the powers on that list. But the purpose of the enumeration of executive powers in
         Article II was not to define and cabin the grant in the Vesting Clause. Rather, the
         Framers unbundled some plenary powers that had traditionally been regarded as
         “executive,” assigning elements of those powers to Congress in Article I, while
         expressly reserving other elements as enumerated executive powers in Article II.
         So, for example, the King’s traditional power to declare war was given to Con-
         gress under Article I, while the Commander-in-Chief authority was expressly
         reserved to the President in Article II. Further, the Framers altered other plenary
         powers of the King, such as treaties and appointments, assigning the Senate a
         share in them in Article II itself.10 Thus, the enumeration in Article II marks the
         points at which several traditional executive powers were diluted or reallocated.
         Any other unenumerated executive powers, however, were conveyed to the
         President by the Vesting Clause.
              There can be little doubt that the decision to deploy military force is “execu-
         tive” in nature, and was traditionally so regarded. It calls for action and energy in
         execution, rather than the deliberate formulation of rules to govern the conduct of
         private individuals. Moreover, the Framers understood it to be an attribute of the
         executive. “The direction of war implies the direction of the common strength,”
         wrote Alexander Hamilton, “and the power of directing and employing the
         common strength forms a usual and essential part in the definition of the executive
         authority.” The Federalist No. 74, at 447 (Alexander Hamilton) (Clinton Rossiter
         ed., 1961). As a result, to the extent that the constitutional text does not explicitly
         allocate the power to initiate military hostilities to a particular branch, the Vesting
         Clause provides that it remain among the President’s unenumerated powers.

             10
                Thus, Article II’s enumeration of the Treaty and Appointments Clauses only dilutes the unitary
         nature of the Executive Branch in regard to the exercise of those powers, rather than transforming them
         into quasi-legislative functions. See Constitutionality of Proposed Conditions to Senate Consent to the
         Interim Convention on Conservation of North Pacific Fur Seals, 10 Op. O.L.C. 12, 17 (1986)
         (“Nothing in the text of the Constitution or the deliberations of the Framers suggests that the Senate’s
         advice and consent role in the treaty-making process was intended to alter the fundamental constitu-
         tional balance between legislative authority and executive authority.”).

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                 Fourth, depriving the President of the power to decide when to use military
             force would disrupt the basic constitutional framework of foreign relations. From
             the very beginnings of the Republic, the vesting of the executive, Commander-in-
             Chief, and treaty powers in the Executive Branch has been understood to grant the
             President plenary control over the conduct of foreign relations. As Secretary of
             State Thomas Jefferson observed during the first Washington Administration,
             “[t]he constitution has divided the powers of government into three branches [and]
             has declared that the executive powers shall be vested in the president, submitting
             only special articles of it to a negative by the senate.” Thomas Jefferson, Opinion
             on the Powers of the Senate (1790), reprinted in 5 The Writings of Thomas
             Jefferson at 161 (Paul L. Ford ed., 1895). Due to this structure, Jefferson contin-
             ued, “[t]he transaction of business with foreign nations is executive altogether; it
             belongs, then, to the head of that department, except as to such portions of it as are
             specially submitted to the senate. Exceptions are to be construed strictly.” Id. In
             defending President Washington’s authority to issue the Neutrality Proclamation,
             Alexander Hamilton came to the same interpretation of the President’s foreign
             affairs powers. According to Hamilton, Article II “ought . . . to be considered as
             intended . . . to specify and regulate the principal articles implied in the definition
             of Executive Power; leaving the rest to flow from the general grant of that power.”
             Alexander Hamilton, Pacificus No. 1 (1793), reprinted in 15 The Papers of
             Alexander Hamilton at 33, 39 (Harold C. Syrett et al. eds., 1969). As future Chief
             Justice John Marshall famously declared a few years later, “The President is the
             sole organ of the nation in its external relations, and its sole representative with
             foreign nations . . . . The [executive] department . . . is entrusted with the whole
             foreign intercourse of the nation . . . .” 10 Annals of Cong. 613-14 (1800). Given
             the agreement of Jefferson, Hamilton, and Marshall, it has not been difficult for
             the Executive Branch consistently to assert the President’s plenary authority in
             foreign affairs ever since.
                 On the relatively few occasions where it has addressed foreign affairs, the
             Supreme Court has agreed with the Executive Branch’s consistent interpretation.
             Conducting foreign affairs and protecting the national security are, as the Supreme
             Court has observed, “‘central’ Presidential domains.” Harlow v. Fitzgerald, 457
             U.S. 800, 812 n.19 (1982). The President’s constitutional primacy flows from both
             his unique position in the constitutional structure, and from the specific grants of
             authority in Article II that make the President both the Chief Executive of the
             Nation and the Commander in Chief. See Nixon v. Fitzgerald, 457 U.S. 731, 749-
             50 (1982). Due to the President’s constitutionally superior position, the Supreme
             Court has consistently “recognized ‘the generally accepted view that foreign
             policy [is] the province and responsibility of the Executive.’” Dep’t of Navy v.
             Egan, 484 U.S. 518, 529 (1988) (quoting Haig v. Agee, 453 U.S. at 293-94). “The
             Founders in their wisdom made [the President] not only the Commander-in-Chief
             but also the guiding organ in the conduct of our foreign affairs,” possessing “vast

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         powers in relation to the outside world.” Ludecke v. Watkins, 335 U.S. 160, 173
         (1948). This foreign affairs power is exclusive: it is “the very delicate, plenary and
         exclusive power of the President as sole organ of the federal government in the
         field of international relations—a power which does not require as a basis for its
         exercise an act of Congress.” United States v. Curtiss-Wright Export Corp., 299
         U.S. 304, 320 (1936).
             Conducting military hostilities is a central tool for the exercise of the Presi-
         dent’s plenary control over the conduct of foreign policy. There can be no doubt
         that the use of force protects the Nation’s security and helps it achieve its foreign
         policy goals. Construing the Constitution to grant such power to another branch
         could prevent the President from exercising his core constitutional responsibilities
         in foreign affairs. Even in the cases in which the Supreme Court has limited
         executive authority, it has also emphasized that we should not construe legislative
         prerogatives to prevent the Executive Branch “from accomplishing its constitu-
         tionally assigned functions.” Nixon v. Adm’r of Gen. Servs., 433 U.S. 425, 443
         (1977).

                                                       II.

            Executive Branch Construction and Practice. The position we take here has
         long represented the view of the Executive Branch and of the Department of
         Justice. Attorney General (later Justice) Robert Jackson formulated the classic
         statement of the Executive Branch’s understanding of the President’s military
         powers in 1941:

                     Article II, section 2, of the Constitution provides that the Presi-
                  dent “shall be Commander in Chief of the Army and Navy of the
                  United States.” By virtue of this constitutional office he has supreme
                  command over the land and naval forces of the country and may
                  order them to perform such military duties as, in his opinion, are
                  necessary or appropriate for the defense of the United States. These
                  powers exist in time of peace as well as in time of war.

                      ....

                     Thus the President’s responsibility as Commander in Chief
                  embraces the authority to command and direct the armed forces in
                  their immediate movements and operations designed to protect the
                  security and effectuate the defense of the United States. . . . [T]his
                  authority undoubtedly includes the power to dispose of troops and
                  equipment in such manner and on such duties as best to promote the
                  safety of the country.

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             Training of British Flying Students in the United States, 40 Op. Att’y Gen. 58, 61-
             62 (1941).11 Other Attorneys General have defended similar accounts of the
             President’s constitutional powers and duties, particularly in times of unforeseen
             emergencies.
                Attorney General William P. Barr, quoting the opinion of Attorney General
             Jackson just cited, advised the President in 1992 that “[y]ou have authority to
             commit troops overseas without specific prior Congressional approval ‘on
             missions of good will or rescue, or for the purpose of protecting American lives or
             property or American interests.’” Authority to Use United States Military Forces
             in Somalia, 16 Op. O.L.C. 6, 6 (1992) (citation omitted).
                Attorney General (later Justice) Frank Murphy, though declining to define
             precisely the scope of the President’s independent authority to act in emergencies
             or states of war, stated that:

                      the Executive has powers not enumerated in the statutes—powers
                      derived not from statutory grants but from the Constitution. It is uni-
                      versally recognized that the constitutional duties of the Executive
                      carry with them the constitutional powers necessary for their proper
                      performance. These constitutional powers have never been specifi-
                      cally defined, and in fact cannot be, since their extent and limitations
                      are largely dependent upon conditions and circumstances. . . . The
                      right to take specific action might not exist under one state of facts,
                      while under another it might be the absolute duty of the Executive to
                      take such action.

             Request of the Senate for an Opinion as to the Powers of the President “In Emer-
             gency or State of War,” 39 Op. Att’y Gen. 343, 347-48 (1939).
                 Attorney General Thomas Gregory opined in 1914 that “[i]n the preservation of
             the safety and integrity of the United States and the protection of its responsibili-
             ties and obligations as a sovereignty, [the President’s] powers are broad.” Censor-
             ship of Radio Stations, 30 Op. Att’y Gen. 291, 292 (1914).
                 Finally, in 1898, Acting Attorney General John K. Richards wrote:

                      The preservation of our territorial integrity and the protection of our
                      foreign interests is intrusted, in the first instance, to the President. . . .
                      In the protection of these fundamental rights, which are based upon
                      the Constitution and grow out of the jurisdiction of this nation over

                 11
                    At the time Attorney General Jackson delivered his opinion, the United States was a neutral, and
             thus his conclusions about the President’s powers did not rest on any special considerations that might
             apply in time of war. Although he stated that he was “inclined to the opinion” that a statute (the Lend-
             Lease Act) authorized the decision under review, Jackson expressly based his conclusion on the
             President’s constitutional authority. 40 Op. Att’y Gen. at 61.

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                  its own territory and its international rights and obligations as a dis-
                  tinct sovereignty, the President is not limited to the enforcement of
                  specific acts of Congress. [The President] must preserve, protect, and
                  defend those fundamental rights which flow from the Constitution
                  itself and belong to the sovereignty it created.

         Foreign Cables, 22 Op. Att’y Gen. 13, 25-26 (1898). Acting Attorney General
         Richards cited, among other judicial decisions, Cunningham v. Neagle, 135 U.S. 1,
         64 (1890), in which the Supreme Court stated that the President’s power to enforce
         the laws of the United States “include[s] the rights, duties and obligations growing
         out of the constitution itself, our international relations, and all the protection
         implied by the nature of the government under the constitution.”
            Opinions of the Office of Legal Counsel. Our Office has taken the position in
         recent Administrations, including those of Presidents Clinton, Bush, Reagan,
         Carter, and Nixon, that the President may unilaterally deploy military force in
         order to protect the national security and interests of the United States.
            In 1995, we opined that the President, “acting without specific statutory author-
         ization, lawfully may introduce United States ground troops into Bosnia and
         Herzegovina . . . to help the North Atlantic Treaty Organization . . . ensure
         compliance with the recently negotiated peace agreement.” Proposed Deployment
         of United States Armed Forces in Bosnia and Herzegovina, 19 Op. O.L.C. 327,
         327 (1995) (the “Bosnia Opinion”). We interpreted the WPR to “lend[] support to
         the . . . conclusion that the President has authority, without specific statutory
         authorization, to introduce troops into hostilities in a substantial range of circum-
         stances.” Id. at 335.
            In Deployment of United States Armed Forces into Haiti, 18 Op. O.L.C. 173
         (1994), we advised that the President had the authority unilaterally to deploy some
         20,000 troops into Haiti. We relied in part on the structure of the WPR, which we
         argued “makes sense only if the President may introduce troops into hostilities or
         potential hostilities without prior authorization by the Congress.” Id. at 175-76.
         We further argued that “in establishing and funding a military force that is capable
         of being projected anywhere around the globe, Congress has given the President,
         as Commander in Chief, considerable discretion in deciding how that force is to be
         deployed.” Id. at 177. We also cited and relied upon the past practice of the
         Executive Branch in undertaking unilateral military interventions:

                     In 1940, after the fall of Denmark to Germany, President Franklin
                  Roosevelt ordered United States troops to occupy Greenland, a Dan-
                  ish possession in the North Atlantic of vital strategic interest to the
                  United States. . . . Congress was not consulted or even directly
                  informed. . . . Later, in 1941, the President ordered United States
                  troops to occupy Iceland, an independent nation, pursuant to an

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                      agreement between himself and the Prime Minister of Iceland. The
                      President relied upon his authority as Commander in Chief, and noti-
                      fied Congress only after the event. . . . More recently, in 1989, at the
                      request of President Corazon Aquino, President Bush authorized mil-
                      itary assistance to the Philippine government to suppress a coup
                      attempt.

             Id. at 178.
                 In Authority to Use United States Military Forces in Somalia, 16 Op. O.L.C. 6
             (1992), our Office advised that the President had the constitutional authority to
             deploy United States Armed Forces into Somalia in order to assist the United
             Nations in ensuring the safe delivery of relief to distressed areas of that country.
             We stated that “the President’s role under our Constitution as Commander in Chief
             and Chief Executive vests him with the constitutional authority to order United
             States troops abroad to further national interests such as protecting the lives of
             Americans overseas.” Id. at 8. Citing past practice (further discussed below), we
             pointed out that

                      [f]rom the instructions of President Jefferson’s Administration to
                      Commodore Richard Dale in 1801 to “chastise” Algiers and Tripoli
                      if they continued to attack American shipping, to the present, Presi-
                      dents have taken military initiatives abroad on the basis of their con-
                      stitutional authority. . . . Against the background of this repeated past
                      practice under many Presidents, this Department and this Office have
                      concluded that the President has the power to commit United States
                      troops abroad for the purpose of protecting important national inter-
                      ests.

             Id. at 9 (citations omitted).
                 In Overview of the War Powers Resolution, 8 Op. O.L.C. 271, 275 (1984), we
             noted that “[t]he President’s authority to deploy armed forces has been exercised
             in a broad range of circumstances [in] our history.”
                 In Presidential Power to Use the Armed Forces Abroad Without Statutory
             Authorization, 4A Op. O.L.C. 185, 187 (1980), we stated that

                      [o]ur history is replete with instances of presidential uses of military
                      force abroad in the absence of prior congressional approval. This
                      pattern of presidential initiative and congressional acquiescence may
                      be said to reflect the implicit advantage held by the executive over
                      the legislature under our constitutional scheme in situations calling
                      for immediate action. Thus, constitutional practice over two centu-
                      ries, supported by the nature of the functions exercised and by the

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                  few legal benchmarks that exist, evidences the existence of broad
                  constitutional power.

         In light of that understanding, we advised that the President had independent
         constitutional authority unilaterally to order “(1) deployment abroad at some risk
         of engagement—for example, the current presence of the fleet in the Persian Gulf
         region; (2) a military expedition to rescue the hostages or to retaliate against Iran if
         the hostages are harmed; (3) an attempt to repel an assault that threatens our vital
         interests in that region.” Id. at 185-86. See also Presidential Powers Relating to
         the Situation in Iran, 4A Op. O.L.C. 115, 121 (1979) (“It is well established that
         the President has the constitutional power as Chief Executive and Commander-in-
         Chief to protect the lives and property of Americans abroad. This understanding is
         reflected in judicial decisions . . . and recurring historic practice which goes back
         to the time of Jefferson.”).
             Finally, in the Rehnquist Memo, we concluded that the President as Comm-
         ander in Chief had the authority “to commit military forces of the United States to
         armed conflict . . . to protect the lives of American troops in the field.” Id. at 8.
             Judicial Construction. Judicial decisions since the beginning of the Republic
         confirm the President’s constitutional power and duty to repel military action
         against the United States through the use of force, and to take measures to deter
         the recurrence of an attack. As Justice Joseph Story said long ago, “[i]t may be fit
         and proper for the government, in the exercise of the high discretion confided to
         the executive, for great public purposes, to act on a sudden emergency, or to
         prevent an irreparable mischief, by summary measures, which are not found in the
         text of the laws.” The Apollon, 22 U.S. (9 Wheat.) 362, 366-67 (1824). The
         Constitution entrusts the “power [to] the executive branch of the government to
         preserve order and insure the public safety in times of emergency, when other
         branches of the government are unable to function, or their functioning would
         itself threaten the public safety.” Duncan v. Kahanamoku, 327 U.S. 304, 335
         (1946) (Stone, C.J., concurring).
             If the President is confronted with an unforeseen attack on the territory and
         people of the United States, or other immediate, dangerous threat to American
         interests and security, the courts have affirmed that it is his constitutional respon-
         sibility to respond to that threat with whatever means are necessary, including the
         use of military force abroad. See, e.g., Prize Cases, 67 U.S. at 635 (“If a war be
         made by invasion of a foreign nation, the President is not only authorized but
         bound to resist force by force . . . without waiting for any special legislative
         authority.”); Kahanamoku, 327 U.S. at 336 (Stone, C.J., concurring) (“Executive
         has broad discretion in determining when the public emergency is such as to give
         rise to the necessity” for emergency measures); United States v. Smith, 27 F. Cas.
         1192, 1230 (C.C.D.N.Y. 1806) (No. 16,342) (Paterson, Circuit Justice) (regardless
         of statutory authorization, it is “the duty . . . of the executive magistrate . . . to

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             repel an invading foe”);12 Mitchell v. Laird, 488 F.2d 611, 613 (D.C. Cir. 1973)
             (“there are some types of war which without Congressional approval, the President
             may begin to wage: for example, he may respond immediately without such
             approval to a belligerent attack”);13 see also Campbell v. Clinton, 203 F.3d 19, 27
             (D.C. Cir.) (Silberman, J. concurring) (“[T]he President has independent authority
             to repel aggressive acts by third parties even without specific statutory authoriza-
             tion.”), cert. denied, 531 U.S. 815 (2000); id. at 40 (Tatel, J., concurring) (“[T]he
             President, as Commander in Chief, possesses emergency authority to use military
             force to defend the nation from attack without obtaining prior congressional
             approval.”); Story, supra note 9, § 1485 (“[t]he command and application of the
             public force . . . to maintain peace, and to resist foreign invasion” are executive
             powers).

                                                               III.

                 The historical practice of all three branches confirms the lessons of the consti-
             tutional text and structure. The normative role of historical practice in constitu-
             tional law, and especially with regard to separation of powers, is well settled.14
             Both the Supreme Court and the political branches have often recognized that
             governmental practice plays a highly significant role in establishing the contours
             of the constitutional separation of powers: “a systematic, unbroken, executive
             practice, long pursued to the knowledge of the Congress and never before
             questioned . . . may be treated as a gloss on ‘executive Power’ vested in the
             President by § 1 of Art. II.” Youngstown Sheet & Tube Co., 343 U.S. at 610-11
             (Frankfurter, J., concurring). Indeed, as the Court has observed, the role of practice
             in fixing the meaning of the separation of powers is implicit in the Constitution
             itself: “‘the Constitution . . . contemplates that practice will integrate the dispersed
             powers into a workable government.’” Mistretta v. United States, 488 U.S. 361,

                 12
                    Justice Paterson went on to remark that in those circumstances “it would I apprehend, be not only
             lawful for the president to resist such invasion, but also to carry hostilities into the enemy’s own
             country.” 27 F. Cas. at 1230.
                 13
                    The court further observed that “in a grave emergency [the President] may, without Congression-
             al approval, take the initiative to wage war. . . . In such unusual situations necessity confers the
             requisite authority upon the President. Any other construction of the Constitution would make it self-
             destructive.” 488 F.2d at 613-14. Accord Massachusetts v. Laird, 451 F.2d at 31 (“[t]he executive may
             without Congressional participation repel attack”).
                 14
                    As the Supreme Court has noted, “the decisions of the Court in th[e] area [of foreign affairs] have
             been rare, episodic, and afford little precedential value for subsequent cases.” Dames & Moore, 453
             U.S. at 661. In particular, the difficulty the courts experience in addressing “the broad range of vitally
             important day-to-day questions regularly decided by Congress or the Executive” with respect to foreign
             affairs and national security makes the judiciary “acutely aware of the necessity to rest [judicial]
             decision[s] on the narrowest possible ground capable of deciding the case.” Id. at 660-61. Historical
             practice and the ongoing tradition of Executive Branch constitutional interpretation therefore play an
             especially important role in this area.

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         381 (1989) (citation omitted). In addition, governmental practice enjoys significant
         weight in constitutional analysis for practical reasons, on “the basis of a wise and
         quieting rule that, in determining . . . the existence of a power, weight shall be
         given to the usage itself—even when the validity of the practice is the subject of
         investigation.” United States v. Midwest Oil Co., 236 U.S. 459, 473 (1915).
             The role of practice is heightened in dealing with issues affecting foreign
         affairs and national security, where “the Court has been particularly willing to rely
         on the practical statesmanship of the political branches when considering constitu-
         tional questions.” Whether Uruguay Round Agreements Required Ratification as a
         Treaty, 18 Op. O.L.C. 232, 234 (1994). “The persistence of these controversies
         (which trace back to the eighteenth century), and the nearly complete absence of
         judicial decisions resolving them, underscore the necessity of relying on congress-
         ional precedent to interpret the relevant constitutional provisions.” Id. at 236.
         Accordingly, we give considerable weight to the practice of the political branches
         in trying to determine the constitutional allocation of warmaking powers between
         them.
             The historical record demonstrates that the power to initiate military hostilities,
         particularly in response to the threat of an armed attack, rests exclusively with the
         President. As the Supreme Court has observed, “[t]he United States frequently
         employs Armed Forces outside this country—over 200 times in our history—for
         the protection of American citizens or national security.” United States v. Verdu-
         go-Urquidez, 494 U.S. 259, 273 (1990). On at least 125 such occasions, the
         President acted without prior express authorization from Congress. See Bosnia
         Opinion, 19 Op. O.L.C. at 331. Such deployments, based on the President’s
         constitutional authority alone, have occurred since the Administration of George
         Washington. See David P. Currie, The Constitution in Congress: Substantive
         Issues in the First Congress, 1789-1791, 61 U. Chi. L. Rev. 775, 816 (1994)
         (“[B]oth Secretary [of War] Knox and [President] Washington himself seemed to
         think that this [Commander-in-Chief] authority extended to offensive operations
         taken in retaliation for Indian atrocities.”) (quoted in Bosnia Opinion, 19 Op.
         O.L.C. at 331 n.4). Perhaps the most significant deployment without specific
         statutory authorization took place at the time of the Korean War, when President
         Truman, without prior authorization from Congress, deployed United States troops
         in a war that lasted for over three years and caused over 142,000 American
         casualties. See Bosnia Opinion, 19 Op. O.L.C. at 331-32 n.5.
             Recent deployments ordered solely on the basis of the President’s constitutional
         authority have also been extremely large, representing a substantial commitment
         of the Nation’s military personnel, diplomatic prestige, and financial resources. On
         at least one occasion, such a unilateral deployment has constituted full-scale war.
         On March 24, 1999, without any prior statutory authorization and in the absence of
         an attack on the United States, President Clinton ordered hostilities to be initiated
         against the Republic of Yugoslavia. The President informed Congress that, in the

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             initial wave of air strikes, “United States and NATO forces have targeted the
             [Yugoslavian] government’s integrated air defense system, military and security
             police command and control elements, and military and security police facilities
             and infrastructure. . . . I have taken these actions pursuant to my constitutional
             authority to conduct U.S. foreign relations and as Commander in Chief and Chief
             Executive.” Letter to Congressional Leaders Reporting on Airstrikes Against
             Serbian Targets in the Federal Republic of Yugoslavia (Serbia and Montenegro),
             1 Pub. Papers of Pres. William J. Clinton 459, 459-60 (Mar. 26, 1999). Bombing
             attacks against targets in both Kosovo and Serbia ended on June 10, 1999,
             seventy-nine days after the war began. More than 30,000 United States military
             personnel participated in the operations; some 800 U.S. aircraft flew more than
             20,000 sorties; more than 23,000 bombs and missiles were used. As part of the
             peace settlement, NATO deployed some 50,000 troops into Kosovo, 7,000 of them
             American.15 In a News Briefing on June 10, 1999, Secretary of Defense William S.
             Cohen summarized the effects of the campaign by saying,

                      [t]hree months ago Yugoslavia was a heavily armed country with a
                      significant air defense system. We reduced that defense system threat
                      by destroying over 80 percent of Yugoslavia’s modern aircraft fight-
                      ers and strategic suface-to-air missiles. NATO destroyed a signifi-
                      cant share of the infrastructure Yugoslavia used to support[] its mili-
                      tary with, we reduced [its] capacity to make ammunition by two-
                      thirds, and we eliminated all of its oil refining capacity and more
                      than 40 percent of its military fuel supplies. Most important, we
                      severely crippled the military forces in Kosovo by destroying more
                      than 50 percent of the artillery and more than one-third of the
                      armored vehicles.1 6

             General Shelton of the Joint Chiefs of Staff reported that “about half of [Yugosla-
             via’s] defense industry has either been damaged or destroyed. . . . [A]viation, 70
             percent; armored vehicle production, 40 [percent]; petroleum refineries, 100
             percent down; explosive production, about 50 percent; and 65 percent of [its]
             ammunition. . . . For the most part Belgrade is a city that’s got about probably 70

                 15
                    See Campbell v. Clinton, 203 F.3d at 40 (Tatel, J., concurring) (quoting testimony of Secretary of
             Defense Cohen that “‘[w]e’re certainly engaged in hostilities [in Yugoslavia], we’re engaged in
             combat’”); Exec. Order No. 13119, 64 Fed. Reg. 18,797 (Apr. 16, 1999) (designating March 24, 1999,
             as “the date of the commencement of combatant activities” in Yugoslavia); John C. Yoo, UN Wars, US
             War Powers, 1 Chi. J. Int’l L. 355 (2000).
                 16
                    Office of the Assistant Secretary of Defense (Public Affairs), DoD News Briefing (June 10, 1999,
             4:05 PM) (remarks of Secretary of Defense Cohen), available at http://www.defense.gov/transcripts/
             transcript.aspx?transcriptid=487 (last visited Apr. 27, 2012).

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         percent without [electrical] power.”17 A report by General Ryan, Air Force Chief
         of Staff, stated that

                     Serbia’s air force is essentially useless and its air defenses are
                  dangerous but ineffective. Military armament production is
                  destroyed. Military supply areas are under siege. Oil refinement has
                  ceased and petroleum storage is systematically being destroyed.
                  Electricity is sporadic, at best. Major transportation routes are cut.

                     NATO aircraft are attacking with impunity throughout the coun-
                  try.18

         Estimates near the time placed the number of Yugoslav military casualties at
         between five and ten thousand.19 In recent decades, no President has unilaterally
         deployed so much force abroad.
            Other recent unilateral deployments have also been significant in military,
         foreign policy, and financial terms. Several such deployments occurred in the
         Balkans in the mid-1990s.2 0 In December 1995, President Clinton ordered the
         deployment of 20,000 United States troops to Bosnia to implement a peace
         settlement. In February 1994, sixty United States warplanes conducted airstrikes
         against Yugoslav targets. In 1993, United States warplanes were sent to enforce a
         no-fly zone over Bosnia; in the same year, the President despatched United States
         troops to Macedonia as part of a United Nations peacekeeping operation.
            Major recent deployments have also taken place in Central America and in the
         Persian Gulf. In 1994, President Clinton ordered some 20,000 United States troops
         to be deployed into Haiti, again without prior statutory authorization from
         Congress, in reliance solely upon his Article II authority. See Deployment of
         United States Armed Forces into Haiti, 18 Op. O.L.C. 173 (1994). On August 8,
         1990, in response to the Iraqi invasion of Kuwait and the consequent threat to
         Saudi Arabia, President Bush ordered the deployment of substantial forces into
         Saudi Arabia in Operation Desert Shield. The forces were equipped for combat
         and included two squadrons of F-15 aircraft and a brigade of the 82d Airborne
         Division; the deployment eventually grew to several hundred thousand. The
         President informed Congress that he had taken these actions “pursuant to my
         constitutional authority to conduct our foreign relations and as Commander in
         Chief.” Letter to Congressional Leaders on the Deployment of United States
         Armed Forces to Saudi Arabia and the Middle East, 2 Pub. Papers of Pres.

             17
                Id. (remarks of General Shelton).
             18
                General Michael E. Ryan, Air Power Is Working in Kosovo, Wash. Post, June 4, 1999, at A35.
             19
                See Nick Cook, War of Extremes, Jane’s Defence Weekly, July 7, 1999, at 21.
             20
                See Yoo, UN Wars, 1 Chi. J. Int’l L. at 359.

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             George Bush 1116, 1116 (Aug. 9, 1990). President Bush also deployed some
             15,000 troops into Panama in December, 1990, for the purpose (among others) of
             protecting Americans living in Panama. See Address to the Nation Announcing
             United States Military Action in Panama, 2 Pub. Papers of Pres. George Bush
             1722 (Dec. 20, 1989); see generally Abraham D. Sofaer, The Legality of the
             United States Action in Panama, 29 Colum. J. Transnat’l L. 281 (1991).
                 Further, when Congress has in fact authorized deployments of troops in hostili-
             ties, past Presidents have taken the position that such legislation, although
             welcome, was not constitutionally necessary. For example, in signing Public Law
             102-01, 105 Stat. 3 (1991), authorizing the use of military force in Operation
             Desert Storm against Iraq, President Bush stated that “my request for congression-
             al support did not, and my signing this resolution does not, constitute any change
             in the longstanding positions of the executive branch on either the President’s
             constitutional authority to use the Armed Forces to defend vital U.S. interests or
             the constitutionality of the War Powers Resolution.” Statement on Signing the
             Resolution Authorizing the Use of Military Force Against Iraq, 1 Pub. Papers of
             Pres. George Bush 40, 40 (Jan. 14, 1991).21 Similarly, President John F. Kennedy
             stated on September 13, 1962, that congressional authorization for a naval
             blockade of Cuba was unnecessary, maintaining that “I have full authority now to
             take such action.” The President’s News Conference of September 13, 1962, Pub.
             Papers of Pres. John F. Kennedy 674, 674 (1962). And in a report to the American
             people on October 22, 1962, President Kennedy asserted that he had ordered the
             blockade “under the authority entrusted to me by the Constitution as endorsed by
             the resolution of the Congress.” Radio and Television Report to the American
             People on the Soviet Arms Buildup in Cuba, Pub. Papers of Pres. John F.
             Kennedy 806, 807 (Oct. 22, 1962) (emphasis added).22 Thus, there is abundant

                 21
                    Further, in a press conference on January 9, 1991, President Bush was asked if he believed that he
             needed congressional authorization in order to begin offensive operations against Iraq. He answered, “I
             don’t think I need it. I think Secretary Cheney expressed it very well the other day. There are different
             opinions on either side of this question, but Saddam Hussein should be under no question on this: I feel
             that I have the authority to fully implement the United Nations resolutions.” The President’s News
             Conference on the Persian Gulf Crisis, 1 Pub. Papers of Pres. George Bush 17, 20 (Jan. 9, 1991).
                 22
                    An unsigned, unaddressed opinion in this Office’s files, entitled Blockade of Cuba, states that
             “the President, in the exercise of his constitutional power as Commander-in-Chief, can order a
             blockade without prior Congressional sanction and without a declaration of war by Congress.” Id. at 9
             (Oct. 19, 1962). Thus, the writers of the memorandum (presumably, either this Office or the State
             Department’s Office of the Legal Adviser) determined that no congressional authorization either
             existed or was necessary for the blockade ordered by President Kennedy.
                 Editor’s Note: Prior to the book publication of this opinion, we consulted with officials at the
             Department of State to determine whether they had any record or evidence of authorship of the
             Blockade of Cuba memorandum. Although they were unable to locate a copy of the memorandum
             itself, they pointed us to declassified records of a meeting held on October 19, 1962 (the same date as
             the memorandum) and attended by a number of top-level administration officials (including Secretary
             of State Dean Rusk, Attorney General Robert Kennedy, and National Security Advisor McGeorge

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         precedent, much of it from recent Administrations, for the deployment of military
         force abroad, including the waging of war, on the basis of the President’s sole
         constitutional authority.
             Several recent precedents stand out as particularly relevant to the situation at
         hand, where the conflict is with terrorists. The first and most relevant precedent is
         also the most recent: the military actions that President William J. Clinton ordered
         on August 20, 1998, against terrorist sites in Afghanistan and Sudan. The second
         is the strike on Iraqi Intelligence Headquarters that President Clinton ordered on
         June 26, 1993. The third is President Ronald Reagan’s action on April 14, 1986,
         ordering United States armed forces to attack selected targets at Tripoli and
         Benghazi, Libya.

                                                           A.

             On August 20, 1998, President Clinton ordered the Armed Forces to strike at
         terrorist-related facilities in Afghanistan and Sudan “because of the threat they
         present to our national security.” Remarks in Martha’s Vineyard, Massachusetts,
         on Military Action Against Terrorist Sites in Afghanistan and Sudan, 2 Pub.
         Papers of Pres. William J. Clinton 1460, 1460 (Aug. 20, 1998). The President
         stated that the purpose of the operation was “to strike at the network of radical
         groups affiliated with and funded by Usama bin Ladin, perhaps the preeminent
         organizer and financier of international terrorism in the world today.” Address to
         the Nation on Military Action Against Terrorist Sites in Afghanistan and Sudan,
         2 Pub. Papers of Pres. William J. Clinton 1460, 1460 (Aug. 20, 1998). The strike
         was ordered in retaliation for the bombings of United States Embassies in Kenya
         and Tanzania, in which bin Laden’s organization and groups affiliated with it were
         believed to have played a key role and which had caused the deaths of some 12
         Americans and nearly 300 Kenyans and Tanzanians, and in order to deter later
         terrorist attacks of a similar kind against United States nationals and others. In his
         remarks at Martha’s Vineyard, President Clinton justified the operation as follows:

         Bundy). See U.S. Dep’t of State, Foreign Relations of the United States, 1961-1963: Volume XI, Cuban
         Missile Crisis and Aftermath, doc. 31 (Edward C. Keefer et al., eds., 1998), available at http://history.
         state.gov/historicaldocuments/frus1961-63v11/d31 (last visited Aug. 3, 2012) (notes of October 19,
         1962 meeting). These records suggest that the memorandum may have been prepared by Leonard
         Meeker, Deputy Legal Adviser for the Department of State, perhaps in consultation with Nicholas
         Katzenbach, Deputy Attorney General and former Assistant Attorney General for the Office of Legal
         Counsel. Mr. Meeker kept notes of the October 19 meeting, which indicate that he presented legal
         analysis paralleling that in the Blockade of Cuba memorandum and concluding that the President could
         respond militarily to the Soviet missile threat without a declaration of war. Mr. Katzenbach also spoke
         at the meeting and concurred with Mr. Meeker that “the President had ample constitutional and
         statutory authority to take any needed military measures.” Id.

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                         President’s Authority to Conduct Military Operations Against Terrorists

                         I ordered this action for four reasons: first, because we have con-
                      vincing evidence these groups played the key role in the Embassy
                      bombings in Kenya and Tanzania; second, because these groups
                      have executed terrorist attacks against Americans in the past; third,
                      because we have compelling information that they were planning
                      additional terrorist attacks against our citizens and others with the
                      inevitable collateral casualties we saw so tragically in Africa; and
                      fourth, because they are seeking to acquire chemical weapons and
                      other dangerous weapons.

             Remarks in Martha’s Vineyard, 2 Pub. Papers of Pres. William J. Clinton at 1460
             (1998). In his Address to the Nation on the same day, the President made clear that
             the strikes were aimed not only at bin Laden’s organization, but at other terrorist
             groups thought to be affiliated with it, and that the strikes were intended as
             retribution for other incidents caused by these groups, and not merely the then-
             recent bombings of the two United States embassies. Referring to the past acts of
             the interlinked terrorist groups, he stated:

                          Their mission is murder and their history is bloody. In recent
                      years, they killed American, Belgian, and Pakistani peacekeepers in
                      Somalia. They plotted to assassinate the President of Egypt and the
                      Pope. They planned to bomb six United States 747’s over the Pacif-
                      ic. They bombed the Egyptian Embassy in Pakistan. They gunned
                      down German tourists in Egypt.

             Address to the Nation, 2 Pub. Papers of Pres. William J. Clinton at 1460-61
             (1998). Furthermore, in explaining why military action was necessary, the
             President noted that “law enforcement and diplomatic tools” to combat terrorism
             had proved insufficient, and that “when our very national security is chal-
             lenged . . . we must take extraordinary steps to protect the safety of our citizens.”
             Id. at 1461. Finally, the President made plain that the action of the two targeted
             countries in harboring terrorists justified the use of military force on their territory:
             “The United States does not take this action lightly. Afghanistan and Sudan have
             been warned for years to stop harboring and supporting these terrorist groups. But
             countries that persistently host terrorists have no right to be safe havens.” Id.
                The terrorist incidents of September 11, 2001, were surely far graver a threat to
             the national security of the United States than the 1998 attacks on our embassies
             (however appalling those events were). The President’s power to respond militari-
             ly to the later attacks must be correspondingly broader. Nonetheless, President
             Clinton’s action in 1998 illustrates some of the breadth of the President’s power to
             act in the present circumstances.
                First, President Clinton justified the targeting of particular groups on the basis
             of what he characterized as “convincing” evidence of their involvement in the

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         embassy attacks. While that is not a standard of proof appropriate for a criminal
         trial, it is entirely appropriate for military and political decisionmaking. Second,
         the President targeted not merely one particular group or leader, but a network of
         affiliated groups. Moreover, he ordered the action not only because of particular
         attacks on United States embassies, but because of a pattern of terrorist activity,
         aimed at both Americans and non-Americans, that had unfolded over several
         years. Third, the President explained that the military action was designed to deter
         future terrorist incidents, not only to punish past ones. Fourth, the President
         specifically justified military action on the territory of two foreign states because
         their governments had “harbor[ed]” and “support[ed]” terrorist groups for years,
         despite warnings from the United States.

                                                           B.

             On June 26, 1993, President Clinton ordered a Tomahawk cruise missile strike
         on Iraqi Intelligence Service (the “IIS”) headquarters in Baghdad. The IIS had
         planned an unsuccessful attempt to assassinate former President Bush in Kuwait in
         April, 1993. Two United States Navy surface ships launched a total of 23 missiles
         against the IIS center.
             In a letter to Congress, the President referred to the failed assassination attempt
         and stated that “[t]he evidence of the Government of Iraq’s violence and terrorism
         demonstrates that Iraq poses a continuing threat to United States nationals.” Letter
         to Congressional Leaders on the Strike on Iraqi Intelligence Headquarters, 1 Pub.
         Papers of Pres. William J. Clinton 940, 940 (June 28, 1993). He based his
         authority to order a strike against the Iraqi government’s intelligence command
         center on “my constitutional authority with respect to the conduct of foreign
         relations and as Commander in Chief,” as well as on the Nation’s inherent right of
         self-defense. Id.
             President Clinton’s order was designed in part to deter and prevent future ter-
         rorist attacks on the United States—and most particularly future assassination
         attempts on former President Bush. Although the assassination attempt had been
         frustrated by the arrest of sixteen suspects before any harm was done, “nothing
         prevented Iraq from directing a second—possibly successful—attempt on Bush’s
         life. Thus, the possibility of another assassination plot was ‘hanging threateningly
         over [Bush’s] head’ and was therefore imminent. By attacking the Iraqi Intelli-
         gence Service, the United States hoped to prevent and deter future attempts to kill
         Bush.”23

             23
                Robert F. Teplitz, Taking Assassination Attempts Seriously: Did the United States Violate Inter-
         national Law in Forcefully Responding to the Iraqi Plot to Kill George Bush?, 28 Cornell Int’l L.J.
         569, 609 (1995) (citation omitted).

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                         President’s Authority to Conduct Military Operations Against Terrorists

                                                             C.

                 On April 14, 1986, President Ronald Reagan, acting on his independent author-
             ity, ordered United States armed forces to engage in military action against the
             government of Colonel Gadhafi of Libya.24 Thirty-two American aircraft attacked
             selected targets at Tripoli and Benghazi, Libya. Libyan officials reported thirty-
             seven people killed and an undetermined number injured. More than sixty tons of
             ordnance were used during the attack.
                 For some time Libya had supported terrorist groups and organizations and
             indeed had itself ordered direct terrorist attacks on the United States.

                      Under Gaddafi, Libya has declared its support of “national liberation
                      movements” and has allegedly financed and trained numerous terror-
                      ist groups and organizations, including Palestinian radicals, Leba-
                      nese leftists, Columbia’s M-19 guerrillas, the Irish Republican
                      Army, anti-Turkish Armenians, the Sandinistas in Nicaragua, Mus-
                      lim rebels in the Philippines, and left-wing extremists in Europe and
                      Japan.25

             It had harbored a variety of terrorists, including Abu Nidal and the three surviving
             members of the Black September group that had killed eleven Israeli athletes at the
             1972 Munich Olympic Games.26 Libya’s attacks on the United States included the
             murder of two United States diplomats in Khartoum (1973), the attempted
             assassination of Secretary of State Kissinger (1973), the burning of the United
             States Embassy in Tripoli (1979), the planned assassination of President Reagan,
             Secretary of State Haig, Secretary of Defense Weinberger, and Ambassador to
             Italy Robb (1981), and the hijacking of T.W.A. flight 847 (1985).27 Libya had also
             been linked to terrorist events close to the time of the April, 1986, airstrike in
             which Americans and others had lost their lives. In January, 1986, American
             intelligence tied Libya to the December 27, 1985, bombings at the Rome and
             Vienna airports in which nineteen people, including 5 Americans, had died, and
             one hundred and twelve persons had been injured.
                 The particular event that triggered the President’s military action had occurred
             on April 5, 1986, when a bomb exploded in the “Labelle,” a Berlin discotheque
             frequented by U.S. military personnel. The blast killed three people (two Ameri-
             cans) and injured two hundred and thirty others (including seventy-nine Ameri-

                 24
                    See generally Wallace F. Warriner, U.S.M.C., The Unilateral Use of Coercion Under Interna-
             tional Law: A Legal Analysis of the United States Raid on Libya on April 14, 1986, 37 Naval L. Rev.
             49 (1988); Teplitz, 28 Cornell Int’l L. J. at 583-86.
                 25
                    Teplitz, 28 Cornell Int’l L. J. at 583 n.112.
                 26
                    See id.
                 27
                    See id. at 583 n.113.

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         cans). Intelligence reports indicated that the bombing was planned and executed
         under the direct orders of the Government of Libya. The United States Ambassa-
         dor to the United Nations stated that there was “direct, precise, and irrefutable
         evidence that Libya bears responsibility” for the bombing of the discotheque; that
         the Labelle incident was “only the latest in an ongoing pattern of attacks by Libya”
         against the United States and its allies; and that the United States had made
         “repeated and protracted efforts to deter Libya from its ongoing attacks,” including
         “quiet diplomacy, public condemnation, economic sanctions and demonstrations
         of military force.” U.N. SCOR, 2674th mtg. at 13, 14, U.N. Doc. S/PV.2674 (prov.
         ed. Apr. 15, 1986).
            Like the two unilateral presidential actions discussed above, President Reagan’s
         decision to use armed force in response to a terrorist attack on United States
         military personnel illustrates that the President has independent constitutional
         authority to use such force in the present circumstances.

                                                       IV.

             Our analysis to this point has surveyed the views and practice of the Executive
         and Judicial Branches. In two enactments, the War Powers Resolution and the
         recent Joint Resolution, Congress has also addressed the scope of the President’s
         independent constitutional authority. We think these two statutes demonstrate
         Congress’s acceptance of the President’s unilateral war powers in an emergency
         situation like that created by the September 11 incidents.
             Furthermore, the President can be said to be acting at the apogee of his powers
         if he deploys military force in the present situation, for he is operating both under
         his own Article II authority and with the legislative support of Congress. Under
         the analysis outlined by Justice Jackson in Youngstown Sheet & Tube Co. (and
         later followed and interpreted by the Court in Dames & Moore), the President’s
         power in this case would be “at its maximum,” 343 U.S. at 635 (Jackson, J.,
         concurring), because the President would be acting pursuant to an express
         congressional authorization. He would thus be clothed with “all [authority] that he
         possesses in his own right plus all that Congress can delegate,” id., in addition to
         his own broad powers in foreign affairs under Article II of the Constitution.
             The War Powers Resolution. Section 2(c) of the WPR, reads as follows:

                  The constitutional powers of the President as Commander-in-Chief
                  to introduce United States Armed Forces into hostilities, or into situ-
                  ations where imminent involvement in hostilities is clearly indicated
                  by the circumstances, are exercised only pursuant to (1) a declaration
                  of war, (2) specific statutory authorization, or (3) a national emer-
                  gency created by attack upon the United States, its territories or pos-
                  sessions, or its armed forces.

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             50 U.S.C. § 1541(c) (2000) (emphasis added).
                The Executive Branch consistently “has taken the position from the very begin-
             ning that section 2(c) of the WPR does not constitute a legally binding definition
             of Presidential authority to deploy our armed forces.” Overview of the War Powers
             Resolution, 8 Op. O.L.C. at 274.28 Moreover, as our Office has noted, “even the
             defenders of the WPR concede that this declaration [in section 2(c)]—found in the
             ‘Purpose and Policy’ section of the WPR—either is incomplete or is not meant to
             be binding.” Deployment of United States Armed Forces into Haiti, 18 Op. O.L.C.
             at 176; accord Bosnia Opinion, 19 Op. O.L.C. at 335 (“The executive branch has
             traditionally taken the position that the President’s power to deploy armed forces
             into situations of actual or indicated hostilities is not restricted to the three
             categories specifically marked out by the Resolution.”); Presidential Powers
             Relating to the Situation in Iran, 4A Op. O.L.C. at 121 (“[T]he Resolution’s policy
             statement is not a comprehensive or binding formulation of the President’s powers
             as Commander-in-Chief.”). Nonetheless, section 2(c)(3) correctly identifies one,
             but by no means the only, presidential authority to deploy military forces into
             hostilities.29 In the present circumstances, the statute signifies Congress’s recogni-
             tion that the President’s constitutional authority alone would enable him to take
             military measures to combat the organizations or groups responsible for the
             September 11 incidents, together with any governments that may have harbored or
             supported them.
                Further, Congress’s support for the President’s power suggests no limits on the
             Executive’s judgment whether to use military force in response to the national
             emergency created by those incidents. Section 2(c)(3) leaves undisturbed the
             President’s constitutional authority to determine both when a “national emergen-
             cy” arising out of an “attack against the United States” exists, and what types and
             levels of force are necessary or appropriate to respond to that emergency. Because
             the statute itself supplies no definition of these terms, their interpretation must
             depend on longstanding constitutional practices and understandings. As we have
             shown in parts I-III of this memorandum, constitutional text, structure and practice
             demonstrate that the President is vested with the plenary power to use military

                 28
                    Thus, the State Department took the view, in a letter of November 30, 1973, that section 2(c) was
             a “declaratory statement of policy.” 8 Op. O.L.C. at 274. Further, in 1975, the Legal Adviser to the
             State Department listed six (non-exclusive) situations, not enumerated in section 2(c), in which the
             President had independent constitutional authority to deploy troops without either a declaration of war
             or specific statutory authorization. See id. at 274-75.
                 29
                    We note that section 2(c) cannot itself qualify as a statutory authorization to act in national
             emergencies. It is rather a congressional acknowledgment of the President’s nonstatutory, Article II-
             based powers. Section 8(d)(2) of the WPR, 50 U.S.C. § 1547(d)(2) (2000), specifically provides that
             nothing in the WPR “shall be construed as granting any authority to the President . . . which authority
             he would not have had in the absence of this [joint resolution].”

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         force, especially in the case of a direct attack on the United States. Section 2(c)(3)
         recognizes the President’s broad authority and discretion in this area.
            Given the President’s constitutional powers to respond to national emergencies
         caused by attacks on the United States, and given also that section 2(c)(3) of the
         WPR does not attempt to define those powers, we think that that provision must be
         construed simply as a recognition of, and support for, the President’s pre-existing
         constitutional authority. Moreover, as we read the WPR, action taken by the
         President pursuant to the constitutional authority recognized in section 2(c)(3)
         cannot be subject to the substantive requirements of the WPR, particularly the
         interrelated reporting requirements in section 4 and the “cut off” provisions of
         section 5, 50 U.S.C. §§ 1543-1544.30 Insofar as the Constitution vests the power in
         the President to take military action in the emergency circumstances described by
         section 2(c)(3), we do not think it can be restricted by Congress through, e.g., a
         requirement that the President either obtain congressional authorization for the
         action within a specific time frame, or else discontinue the action. Were this not
         so, the President could find himself unable to respond to an emergency that
         outlasted a statutory cut-off, merely because Congress had failed, for whatever
         reason, to enact authorizing legislation within that period.
            To be sure, some interpreters of the WPR take a broader view of its scope. But
         on any reasonable interpretation of that statute, it must reflect an explicit under-
         standing, shared by both the Executive and Congress, that the President may take
         some military actions—including involvement in hostilities—in response to
         emergencies caused by attacks on the United States. Thus, while there might be
         room for disagreement about the scope and duration of the President’s emergency
         powers, there can be no reasonable doubt as to their existence.
            The Joint Resolution of September 14, 2001. Whatever view one may take of
         the meaning of section 2(c)(3) of the WPR, we think it clear that Congress, in
         enacting the “Joint Resolution [t]o authorize the use of United States Armed
         Forces against those responsible for the recent attacks launched against the United
         States,” Pub. L. No. 107-40, 115 Stat. 224 (2001), has confirmed that the President
         has broad constitutional authority to respond, by military means or otherwise, to
         the incidents of September 11.
            First, the findings in the Joint Resolution include an express statement that “the
         President has authority under the Constitution to take action to deter and prevent
         acts of international terrorism against the United States.” Id. This authority is in

             30
                True, the reporting requirement in section 4(a)(1) purports to apply to any case in which U.S.
         armed forces are introduced into hostilities “[i]n the absence of a declaration of war.” 50 U.S.C.
         § 1543(a)(1). Further, the “cut off” provisions of section 5 are triggered by the report required by
         section 4(a)(1). Thus, the language of the WPR indicates an intent to reach action taken by the
         President pursuant to the authority recognized in section 2(c)(3), if no declaration of war has been
         issued. We think, however, that it would be beyond Congress’s power to regulate the President’s
         emergency authority in the manner prescribed by sections 4(a)(1) and 5.

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                         President’s Authority to Conduct Military Operations Against Terrorists

             addition to the President’s authority to respond to past acts of terrorism. In
             including this statement, Congress has provided its explicit agreement with the
             Executive Branch’s consistent position, as articulated in Parts I-III of this memo-
             randum, that the President has the plenary power to use force even before an attack
             upon the United States actually occurs, against targets and using methods of his
             own choosing.
                Second, Congress also found that there is a “threat to the national security and
             foreign policy of the United States posed by the[] grave acts of violence” on
             September 11, and that “such acts continue to pose an unusual and extraordinary
             threat to the national security and foreign policy” of this country. Insofar as “the
             President’s independent power to act depends upon the gravity of the situation
             confronting the nation,” Youngstown Sheet & Tube, 343 U.S. at 662 (Clark, J.,
             concurring in judgment), these findings would support any presidential determina-
             tion that the September 11 attacks justified the use of military force in response.
             Further, they would buttress any presidential determination that the nation is in a
             state of emergency caused by those attacks. The Constitution confides in the
             President the authority, independent of any statute, to determine when a “national
             emergency” caused by an attack on the United States exists.31 Nonetheless,
             congressional concurrence is welcome in making clear that the branches agree on
             the seriousness of the terrorist threat currently facing the Nation and on the
             justifiability of a military response.
                Third, it should be noted here that the Joint Resolution is somewhat narrower
             than the President’s constitutional authority. The Joint Resolution’s authorization
             to use force is limited only to those individuals, groups, or states that planned,
             authorized, committed, or aided the attacks, and those nations that harbored them.
             It does not, therefore, reach other terrorist individuals, groups, or states, which
             cannot be determined to have links to the September 11 attacks. Nonetheless, the
             President’s broad constitutional power to use military force to defend the Nation,
             recognized by the Joint Resolution itself, would allow the President to take
             whatever actions he deems appropriate to pre-empt or respond to terrorist threats
             from new quarters.

                 31
                    See Prize Cases, 67 U.S. at 670 (whether a state of belligerency justifying a blockade exists is to
             be decided by the President); see also Sterling v. Constantin, 287 U.S. 378, 399 (1932) (“By virtue of
             his duty to ‘cause the laws to be faithfully executed’, the Executive is appropriately vested with the
             discretion to determine whether an exigency requiring military aid for that purpose has arisen.”); Moyer
             v. Peabody, 212 U.S. 78, 83 (1909) (“[T]he governor’s declaration that a state of insurrection existed is
             conclusive of that fact.”); Campbell, 203 F.3d at 26-27 (Silberman, J., concurring) (The Court in the
             Prize Cases “made clear that it would not dispute the President on measures necessary to repel foreign
             aggression.”); cf. Martin v. Mott, 25 U.S. (12 Wheat.) 19, 30 (1827) (President had unreviewable
             discretion to determine when “emergency” existed under statute enabling him to call up militia).

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                                                            V.

             In light of the text, plan, and history of the Constitution, its interpretation by
         both past Administrations and the courts, the longstanding practice of the Execu-
         tive Branch, and the express affirmation of the President’s constitutional authori-
         ties by Congress, we think it beyond question that the President has the plenary
         constitutional power to take such military actions as he deems necessary and
         appropriate to respond to the terrorist attacks upon the United States on September
         11, 2001. Force can be used both to retaliate for those attacks, and to prevent and
         deter future assaults on the Nation. Military actions need not be limited to those
         individuals, groups, or states that participated in the attacks on the World Trade
         Center and the Pentagon: the Constitution vests the President with the power to
         strike terrorist groups or organizations that cannot be demonstrably linked to the
         September 11 incidents, but that, nonetheless, pose a similar threat to the security
         of the United States and the lives of its people, whether at home or overseas.32 In
         both the War Powers Resolution and the Joint Resolution, Congress has recog-
         nized the President’s authority to use force in circumstances such as those created
         by the September 11 incidents. Neither statute, however, can place any limits on
         the President’s determinations as to any terrorist threat, the amount of military
         force to be used in response, or the method, timing, and nature of the response.
         These decisions, under our Constitution, are for the President alone to make.

                                                                     JOHN C. YOO
                                                             Deputy Assistant Attorney General
                                                                 Office of Legal Counsel

             32
                We of course understand that terrorist organizations and their state sponsors operate by secrecy
         and concealment, and that it is correspondingly difficult to establish, by the standards of criminal law
         or even lower legal standards, that particular individuals or groups have been or may be implicated in
         attacks on the United States. Moreover, even when evidence sufficient to establish involvement is
         available to the President, it may be impossible for him to disclose that evidence without compromising
         classified methods and sources, and so damaging the security of the United States. See, e.g., Chicago &
         Southern Air Lines, 333 U.S. at 111 (“The President . . . has available intelligence services whose
         reports are not and ought not to be published to the world.”); see also Ruth Wedgwood, Responding to
         Terrorism: The Strikes Against Bin Laden, 24 Yale J. Int’l L. 559, 568-74 (1999) (analyzing difficulties
         of establishing and publicizing evidence of causation of terrorist incidents). But we do not think that the
         difficulty or impossibility of establishing proof to a criminal law standard (or of making evidence
         public) bars the President from taking such military measures as, in his best judgment, he thinks
         necessary or appropriate to defend the United States from terrorist attacks. In the exercise of his plenary
         power to use military force, the President’s decisions are for him alone and are unreviewable.

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