The Congress shall have power to declare war. Invoked to launch or defend against wars 3 times in the 19th and twice in the 20th century, that Constitutional requirement has become as outdated as a dial telephone used to spread the news of the last one, December 8, 1941.
Once established as the world's supreme superpower, American presidents, beginning with Harry Truman in 1950, decided to abandon the need to ask Congress to declare war. Incredibly, Congress went along with this enormous transfer of the war power to the president. When Truman decided to intervene in the Korean conflict, he simply called it a police action and began a military campaign that took several million Korean lives as well inflicting 128,000 U.S. casualties, of which 36,500 died. That's some 'police action'.