"Article I, Section 8, Clause 11 of the U.S. Constitution grants Congress the power to declare war. The President, meanwhile, derives the power to direct the military after a Congressional declaration of war from Article II, Section 2, which names the President Commander-in-Chief of the armed forces."
But of course you knew that already.  To change or not to change...that is the question.  2/3 of all the states?  Possible, but nowadays?  Hmmm.  And w/ the upcoming changes to SCOTUS.....the originalists will unite.
"The resolution (HR-77)[1991] went out of its way not to be a declaration of war. In fact, other than saying this constitutes authorization under the War Powers Act, it never used the word war at all.  It did cite a U.N. resolution seeking to 'restore international peace and security in that area,' so it was only a declaration of war if you can assume that the opposite of peace is sort of war."
Prior to WPA, USMC could be depl w/out Cong approval, now all svcs.