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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 September 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 committed 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 compelling 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 presupposes 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 constitutional 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-inChief 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 inChief” had met with a situation justifying treating the southern States as belligerents 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

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.”).

This view misreads the constitutional text and 

6 See, e.g., Louis Fisher, Presidential War Power 185-206 (1995); John Hart Ely, War and Responsibility: 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 prohibited 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

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.

If the Framers had wanted to require congressional 

consent before the initiation of military hostilities, they knew how to write such 

provisions.

8

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.

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 transform 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, 

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 proceedings 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 definition 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 Congress 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

There can be little doubt that the decision to deploy military force is “executive” 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.

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.

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 constitutional 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-inChief, 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 continued, “[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 President’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 constitutionally 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 President “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

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).

Other Attorneys General have defended similar accounts of the 

President’s constitutional powers and duties, particularly in times of unforeseen 

emergencies.

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 universally 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 specifically 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 Emergency 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 responsibilities and obligations as a sovereignty, [the President’s] powers are broad.” Censorship 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 LendLease 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 distinct 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 authorization, 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 circumstances.” 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 Danish 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 notified Congress only after the event.... More recently, in 1989, at the 

request of President Corazon Aquino, President Bush authorized military 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, Presidents have taken military initiatives abroad on the basis of their constitutional 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 interests.

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 centuries, 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-inChief 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 Commander 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 responsibility 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

III.

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 authorization.”), 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).

The historical practice of all three branches confirms the lessons of the constitutional text and structure. The normative role of historical practice in constitutional law, and especially with regard to separation of powers, is well settled.14

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.

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, 

13 The court further observed that “in a grave emergency [the President] may, without Congressional 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 selfdestructive.” 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 constitutional 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 congressional 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. Verdugo-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

[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 fighters and strategic suface-to-air missiles. NATO destroyed a significant share of the infrastructure Yugoslavia used to support[] its military with, we reduced [its] capacity to make ammunition by twothirds, 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

In a News Briefing on June 10, 1999, Secretary of Defense William S. 

Cohen summarized the effects of the campaign by saying,

6

General Shelton of the Joint Chiefs of Staff reported that “about half of [Yugoslavia’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

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.

A report by General Ryan, Air Force Chief 

of Staff, stated that 

NATO aircraft are attacking with impunity throughout the country.18

Estimates near the time placed the number of Yugoslav military casualties at 

between five and ten thousand.19

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

In recent decades, no President has unilaterally

deployed so much force abroad.

0

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.

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.

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 hostilities, 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 congressional 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

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).

Thus, there is abundant 

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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I ordered this action for four reasons: first, because we have convincing 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 thenrecent 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 Pacific. 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 challenged . . . 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 militarily 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 terrorist 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 Intelligence 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 International 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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C.

On April 14, 1986, President Ronald Reagan, acting on his independent authority, ordered United States armed forces to engage in military action against the 

government of Colonel Gadhafi of Libya.24

For some time Libya had supported terrorist groups and organizations and 

indeed had itself ordered direct terrorist attacks on the United States.

Thirty-two American aircraft attacked 

selected targets at Tripoli and Benghazi, Libya. Libyan officials reported thirtyseven people killed and an undetermined number injured. More than sixty tons of 

ordnance were used during the attack.

Under Gaddafi, Libya has declared its support of “national liberation 

movements” and has allegedly financed and trained numerous terrorist groups and organizations, including Palestinian radicals, Lebanese leftists, Columbia’s M-19 guerrillas, the Irish Republican 

Army, anti-Turkish Armenians, the Sandinistas in Nicaragua, Muslim 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

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 Americans) and injured two hundred and thirty others (including seventy-nine AmeriLibya 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.

24 See generally Wallace F. Warriner, U.S.M.C., The Unilateral Use of Coercion Under International 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 Ambassador 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 situations 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 emergency created by attack upon the United States, its territories or possessions, 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 beginning 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

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 emergency” 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 

In the present circumstances, the statute signifies Congress’s recognition 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.

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 IIbased 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

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 understanding, 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.

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.

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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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 memorandum, 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 determination 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

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.

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.

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 Executive Branch, and the express affirmation of the President’s constitutional authorities 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

JOHN C. YOO

In 

both the War Powers Resolution and the Joint Resolution, Congress has recognized 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.

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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