Defense Primer: Congress's Constitutional Authority with Regard to the Armed Forces [Updated January 3, 2020] [open pdf - 606KB]
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."
CRS In Focus, IF10535
Congressional Research Service: https://crsreports.congress.gov/