HIS BIG BEAUTIIFUL WAR. . .

I Declare This War

MINE AND MINE ALONE

AND I WILL FIGHT IT

UNTIL I AM LOSING IT

AND THEN I'LL SAY

IT'S WAS THE LIBS FAULT

The U. S. Constitution divides the power to make war between the President and Congress. Congress has the power to declare war. However, the President as Commander in Chief has the authority to direct the military after a declaration of war  or in response to an attack. 

Artticle 1, Section 8  designates the Constitution grants Congress the power to "Declare War."

Article II, Section 2 designates the President as "Commander in Chief of the Army and Navy."

While the President can direct miitary operations, they cannot unilaterally initiate a war without congressional authorization, except  in cases of a direct attack on the United States.

The War Powers Resolution of 1973 further limits the president's power to initiate or escalate military actions without congressional.

Essentially, the Constitutiion requires a balance of power, giving Congress the power to authorize war and the President the power to conduct it.