Congress has several powers related to war and the armed forces. Under the War Powers Clause, only Congress may declare war, but in several cases it has, without declaring war, granted the President the authority to engage in military conflicts. Five wars have been declared in United States' history: the War of 1812, the Mexican–American War, the Spanish–American War, World War I and World War II. Some historians argue that the legal doctrines and legislation passed during the operations against Pancho Villa constitute a sixth declaration of war. Congress may grant letters of marque and reprisal. Congress may establish and support the armed forces, but no appropriation made for the support of the army may be used for more than two years. This provision was inserted because the Framers feared the establishment of a standing army, beyond civilian control, during peacetime. Congress may regulate or call forth the state militias, but the states retain the authority to appoint officers and train personnel. Congress also has exclusive power to make rules and regulations governing the land and naval forces. Although the executive branch and the Pentagon have asserted an ever-increasing measure of involvement in this process, the U.S. Supreme Court has often reaffirmed Congress's exclusive hold on this power (e.g. Burns v. Wilson, 346 U.S. 137 (1953)). Congress used this power twice soon after World War II with the enactment of two statutes: the Uniform Code of Military Justice to improve the quality and fairness of courts martial and military justice, and the Federal Tort Claims Act which among other rights had allowed military service persons to sue for damages until the U.S. Supreme Court repealed that section of the statute in a divisive series of cases, known collectively as the Feres Doctrine.
Congress has the exclusive right to legislate "in all cases whatsoever" for the nation's capital, the District of Columbia. Congress chooses to devolve some of such authority to the elected mayor and council of District of Columbia. Nevertheless, Congress remains free to enact any legislation for the District so long as constitutionally permissible, to overturn any legislation by the city government, and technically to revoke the city government at any time. Congress may also exercise such jurisdiction over land purchased from the states for the erection of forts and other buildings.
Finally, Congress has the power to do whatever is "necessary and proper" to carry out its enumerated powers and, crucially, all others vested in it. This has been interpreted to authorize criminal prosecution of those whose actions have a "substantial effect" on interstate commerce in "Wickard v. Filburn" ; however, Thomas Jefferson, in the Kentucky Resolutions, supported by James Madison, maintained that a penal power could not be inferred from a power to regulate, and that the only penal powers were for treason, counterfeiting, piracy and felony on the high seas, and offenses against the law of nations.
The necessary and proper clause has been interpreted extremely broadly, thereby giving Congress wide latitude in legislation. The first landmark case involving the clause was "McCulloch v. Maryland" (1819), which involved the establishment of a national bank. Alexander Hamilton, in advocating the creation of the bank, argued that there was "a more or less direct" relationship between the bank and "the powers of collecting taxes, borrowing money, regulating trade between the states, and raising and maintaining fleets and navies". Thomas Jefferson countered that Congress's powers "can all be carried into execution without a national bank. A bank therefore is not necessary, and consequently not authorized by this phrase". Chief Justice John Marshall agreed with the former interpretation. Marshall wrote that a Constitution listing "all" of Congress's powers "would partake of a prolixity of a legal code and could scarcely be embraced by the human mind". Since the Constitution could not possibly enumerate the "minor ingredients" of the powers of Congress, Marshall "deduced" that Congress had the authority to establish a bank from the "great outlines" of the general welfare, commerce and other clauses. Under this doctrine of the necessary and proper clause, Congress has sweepingly broad powers (known as implied powers) not explicitly enumerated in the Constitution. However, the Congress cannot enact laws solely on the implied powers, any action must be necessary and proper in the execution of the enumerated powers.
The ninth section of Article One places limits on Congress' powers:
The first clause in this section prevents Congress from passing any law that would restrict the importation of slaves into the United States prior to 1808. Congress could however, levy a "Per capita" duty of up to ten dollars for each slave imported into the country. This clause was further entrenched into the Constitution by Article V, where it is explicitly shielded from constitutional amendment prior to 1808. On January 1, 1808, the first day it was permitted to do so, Congress approved legislation prohibiting the importation of slaves into the United States.
A writ of "habeas corpus" is a legal action against unlawful detainment that commands a law enforcement agency or other body that has a person in custody to have a court inquire into the legality of the detention. The court may order the person released if the reason for detention is deemed insufficient or unjustifiable. The Constitution further provides that the privilege of the writ of "habeas corpus" may not be suspended "unless when in cases of rebellion or invasion the public safety may require it". In "Ex parte Milligan" (1866), the Supreme Court ruled that the suspension of "habeas corpus" in a time of war was lawful, but military tribunals did not apply to citizens in states that had upheld the authority of the Constitution and where civilian courts were still operating.
A bill of attainder is a law by which a person is immediately convicted without trial. An "ex post facto" law is a law which applies retroactively, punishing someone for an act that was only made criminal after it was done. The "ex post facto" clause does not apply to civil matters.
Section Nine reiterates the provision from Section Two that direct taxes must be apportioned by state populations. This clause was also explicitly shielded from constitutional amendment prior to 1808 by Article V. In 1913, the 16th Amendment exempted income taxes from this clause. Furthermore, no tax may be imposed on exports from any state. Congress may not, by revenue or commerce legislation, give preference to ports of one state over those of another; neither may it require ships from one state to pay duties in another. All funds belonging to the Treasury may not be withdrawn except according to law. Modern practice is that Congress annually passes a number of appropriations bills authorizing the expenditure of public money. The Constitution requires that a regular statement of such expenditures be published.
The Title of Nobility Clause prohibits Congress from granting any title of nobility. In addition, it specifies that no civil officer may accept, without the consent of Congress, any gift, payment, office or title from a foreign ruler or state. However, a U.S. citizen may receive foreign office before or after their period of public service.