http://www.law.emory.edu/cms/site/index.php?id=3081#7642US Constitution: legislative branch
Clause 11:
To declare War, grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water;
Clause 12:
To raise and support Armies, but no Appropriation of Money to that Use shall be for a longer Term than two Years;Clause 13:
To provide and maintain a Navy;
Clause 14:
To make Rules for the Government and Regulation of the land and naval Forces;
Clause 15:
To provide for calling forth the Militia to execute the Laws of the Union, suppress Insurrections and repel Invasions;
Clause 16:
To provide for organizing, arming, and disciplining, the Militia, and for governing such Part of them as may be employed in the Service of the United States, reserving to the States respectively, the Appointment of the Officers, and the Authority of training the Militia according to the discipline prescribed by Congress;
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The War Powers Act of 1973
http://www.cs.indiana.edu/statecraft/warpow.htmlPURPOSE AND POLICY
SEC. 2. (a) It is the purpose of this joint resolution to fulfill the intent of the framers of the Constitution of the United States and insure that the collective judgement of both the Congress and the President will apply to the introduction of United States Armed Forces into hostilities, or into situations where imminent involvement in hostilities is clearly indicate by the circumstances, and to the continued use of such forces in hostilities or in such situations. SEC. 2. (b) Under article I, section 8, of the Constitution, it is specifically provided that the Congress shall have the power to make all laws necessary and proper for carrying into execution, not only its own powers but also all other powers vested by the Constitution in the Government of the United States, or in any department or officer thereof.
SEC. 2. (c) 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.
CONSULTATION
SEC. 3. The President in every possible instance shall consult with Congress before introducing United States Armed Forces into hostilities or into situation where imminent involvement in hostilities is clearly indicated by the circumstances, and
after every such introduction shall consult regularly with the Congress until United States Armed Forces are no longer engaged in hostilities or have been removed from such situations. REPORTING
Sec. 4. (a) In the absence of a declaration of war, in any case in which United States Armed Forces are introduced--
(1) into hostilities or into situations where imminent involvement in hostilities is clearly indicated by the circumstances;
(2) into the territory, airspace or waters of a foreign nation, while equipped for combat, except for deployments which relate solely to supply, replacement, repair, or training of such forces; or
(3) (A) the circumstances necessitating the introduction of United States Armed Forces;
(B) the constitutional and legislative authority under which such introduction took place; and
(C) the estimated scope and duration of the hostilities or involvement.
Sec. 4. (b) The President shall provide such other information as the Congress may request in the fulfillment of its constitutional responsibilities with respect to committing the Nation to war and to the use of United States Armed Forces abroad.
Sec. 4. (c) Whenever United States Armed Forces are introduced into hostilities or into any situation described in subsection (a) of this section, the President shall, so long as such armed forces continue to be engaged in such hostilities or situation, report to the Congress periodically on the status of such hostilities or situation as well as on the scope and duration of such hostilities or situation, but in no event shall he report to the Congress less often than once every six months.