"Two separate but closely related issues confront Congress each time the President introduces armed forces into a situation abroad that conceivably could lead to their involvement in hostilities. One issue concerns the division of war powers between the President and Congress, whether the use of armed forces falls within the purview of the congressional power to declare war and the War Powers Resolution (WPR). The other issue is whether or not Congress concurs in the wisdom of the action. This report does not deal with the substantive merits of using armed forces in specific cases, but rather with congressional authorization for military action, and the application and effectiveness of the WPR. The purpose of the WPR (P.L. 93-148, passed over President Nixon's veto on November 7, 1973) is to ensure that Congress and the President share in making decisions that may get the United States involved in hostilities. Compliance becomes an issue whenever the President introduces U.S. forces abroad in situations that might be construed as hostilities or imminent hostilities. Criteria for compliance include prior consultation with Congress, fulfillment of the reporting requirements, and congressional authorization. If the President has not complied fully, the issue becomes what action Congress should take to bring about compliance or to influence U.S. policy. A related issue has been congressional authorization of U.N. peacekeeping or other U.N.-sponsored actions."
CRS Report for Congress, RL33532
U.S. Department of State, Foreign Press Centers: http://fpc.state.gov/