In fact, in 1941, the Congress DIRECTED President Roosevelt to wage war on Japan:
"...the President is hereby authorized and directed to employ the entire naval and military forces of the United States and the resources of the Government to carry on war against the Imperial Government of Japan..."
What a lot of folks do not realize is the complete wartime powers given to the President under a declaration of war.
Do you want to give almost unlimited arrest and detainment authority to this President?
No thank you.