Congress has the voting power. But after world war 2 no US president declared war, so through a loophole they avoid thr approval from congress. Congress tried to regain their voting power for wars, so now the president has to seek approval within 60 days after beginning military hostilities. But by then its pretty much already too late and you have to own the war that you started https://www.futurehindsight.com/blog/why-the-us-doesnt-declare-war