The Constitution's text is quite plain with respect to one mechanism by which Congress might give legal effect to whatever judgement it makes: Congress's spending powers. Congress clearly may cut off funds entirely and bring an armed conflict to an end. It may also take the intermediate step of providing that the President may not use military appropriations to alter the scope of nature of the conflict that Congress has authorized and funded, such as by prohibiting the President from using appropriated funds to increase troop levels or broaden a conflict into additional nations or territories.

The Constitution expressly grants Congress extensive powers relating to war, beyond the well-known appropriations power and the power to declare war. Specifically, the Constitution authorizes Congress to:

• Lay and collect taxes, duties, imposts and excises, to pay the debts and provide for the common defence and general welfare of the United States
• Define and punish piracies and felonies committed on the high seas and offenses against the law of nations
• Declare war, grant letters of marque and reprisal, and make rules concerning captures on land and water
• Raise and support armies, but no appropriation of money to that use shall be for a longer term than two years
• Provide and maintain a navy
• Make rules for the government and regulation of the land and naval forces
• Provide for calling forth the militia to execute the laws of the union, suppress insurrections, and repel invasions
• 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
• Make all laws which shall be necessary and proper for carrying into execution the foregoing powers, and all other powers vested by this Constitution in the Government of the United States or in any department of officer thereof.

These provisions plainly set forth an extensive role for Congress that goes far beyond the initial decision to declare war and subsequent decisions regarding its funding. This mass of war powers confers on Congress an ongoing regulatory authority with respect to the war. Indeed, these powers are so extensive that Chief Justice John Marshall opined... that "The whole powers of war (are), by the Constitution of the United States, vested in Congress...." As Commander in Chief, the President's role is to prosecute the war that Congress has authorized within the legitimate parameters Congress sets forth. Congress has exercised precisely this power to define the parameters of armed conflict or war on a number of occasions, some of which concern recent military engagements.

Thus, Congress may limit the scope of the present Iraq War by either of two mechanisms. First, it may directly define limits on the scope of that war, such as by imposing geographic restrictions or a ceiling on the number of troops assigned to that conflict. Second, it may achieve the same objective by enacting appropriations restrictions that limit the use of appropriated funds. Indeed, the reason that the Constitution explicitly limits appropriations for the Army to two years is in order to ensure that Congress oversees ongoing military engagements.