The U.S. Constitution rightly makes the president the commander-in-chief of the military (Article One, Section 2), but in order that he properly and effectively deploy the military it also requires him first to persuade Congress to vote upon and declare war (Article Two, Section 8), which means the President must cite the provocation, name the enemy, and project a plausible path to victory.
FORBES: The Proliferation of Illegal Wars Erodes American Values