“War is up to the president, and perhaps up to Congress,” Mattis said. 

Perhaps Mr. Mattis, the Secretary of Defense, second in command of the largest military in the world, ought to review the rules his office operates under:

Article I, Section 8, Clause 11 of the U.S. Constitution grants CONGRESS [caps for emphesis] 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.