"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. The other issue is whether Congress concurs in the wisdom of the action. This issue brief does not deal with the substantive merits of using armed forces in specific cases, but rather with the congressional authorization for the action and the application and effectiveness of the War Powers Resolution. The purpose of the War Powers Resolution (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 U.S. 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. [...] A longer-term issue is whether the War Powers Resolution is an appropriate and effective means of assuring congressional participation in actions that might get the United States involved in war. Some observers contend that the War Powers Resolution has not significantly increased congressional participation, while others emphasize that it has promoted consultation and served as leverage. Proposals have been made to strengthen, change, or repeal the resolution. None have been enacted to date."
U.S. Dept. of State, Foreign Press Centers: http://fpc.state.gov/