Defense Primer: Congress's Constitutional Authority with Regard to the Armed Forces [December 7, 2016] [open pdf - 336KB]
From the Document: "The power 'To declare War' has long been construed to mean not only that Congress can formally take the nation into war, but also that it can authorize the use of the Armed Forces for military expeditions that may not amount to war. While a restrictive interpretation of the power 'To declare War' is possible, for example, by viewing the Framers' use of the verb 'to declare' rather than 'to make' as an indication of an intent to limit Congress's ability to affect the course of a war once it is validly commenced, Congress's other powers over the use of the military would likely fill any resulting void. In practice, courts have not sought to delineate the boundaries of each clause relating to war powers or identify gaps between them to find specific powers that are denied to Congress. However, the Supreme Court has suggested that Congress might overstep its bounds into presidential territory if it were to interfere with the conduct of military operations. Debates relating to legislation and regarded by some as interfering with the President's Commander-in-Chief authority are frequently framed in terms of legislative meddling in military operations, but the line between regulating the Armed Forces and directing campaigns has proved elusive. Congress has also used its authority to provide for the organization and regulation of the Armed Forces to determine how military personnel are to be organized and employed. For example, earliest statutes prescribed in fairly precise terms how military units were to be formed and commanded."
CRS In Focus, IF10535
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html