Section 1541(c) of the War Powers Act says that the President can send our forces into hostilities in three cases: Congressionally declared war, Specifically, statutorily authorized use of military force, When there is a national emergency created by an attack on the United States. When this happens, the President has to tell Congress the justification for the action within 48 hours and that where an action is not authorized by Congress, it must end in 60 days.