Congress has tended in recent years to tell the President to "do the right thing" and leave him alone with the Joint Chiefs while they look on from the sidelines and wash their hands, the specific enumeration in Article One, Section Eight notwithstanding.
Wikipedia tells me, "The last time the United States formally declared war, using specific terminology, on any nation was in 1942, when war was declared against Axis-allied Hungary, Bulgaria, and Romania...." Congress, it appears, has been asleep at the switch or just waving the Executive Branch on by, all through the Korean Conflict, the Vietnam War (euphemism bedammed withal), Grenada, Panama (okay, that was more like a drug bust) and the specific manifestations of the War On a Noun in Iraq and Afghanistan, to ignore U. N. "peacekeeping" expeditions and name a few war-ish actions that spring to mind.
Then an extremely polarizing President authorized the military killing a man who was a known sponsor of terrorism. True, he was very highly placed in the Iranian government -- and the person in day-to-day charge of their version of the SOE. Congress -- especially the Democrats in Congress -- is not happy. Nope, they are riled and they're talking about reining him in, starting some time next week.
And never mind that it's been Congress who have let the reins out all this while.
Who knows? This might even spell the beginning of a whole new era of Congressional responsibility! But I think you'd be wise to not bet any more money that you can afford to lose on that.