Congress need not issue a formal declaration to authorize force. An authorization for use of military force can permit operations within defined objectives, geography, targets, or time. Congress also shapes military action through appropriations, force structure, regulation of the armed forces, and repeal or revision of prior authorization.

The president's Commander in Chief authority includes operational command and a disputed sphere of unilateral action, especially in emergencies and limited deployments. The precise boundary between initiation and command has remained contested across the branches and is not captured by saying either institution "controls war."

The War Powers Resolution requires consultation where possible and a written report within forty-eight hours after covered introductions of forces. The reporting triggers include hostilities or clearly imminent hostilities, specified combat-equipped deployments into foreign territory, airspace, or waters, and substantial enlargements of combat-equipped forces already abroad. After a report under the hostilities provision is submitted or legally required, the statute ordinarily requires termination within sixty days unless Congress declares war, specifically authorizes the action, extends the period by law, or cannot meet because of an armed attack. The president may certify in writing that unavoidable military necessity requires up to thirty additional days for safe withdrawal. Presidents have challenged features of this statutory framework, so distinguish what the law requires from unresolved constitutional objections.

Video lesson: Congressional Decisions: Crash Course Government and Politics #10