https://www.nationalreview.com/2020/01/qasem-soleimani-strike-president-trump-has-constitution-precedent-on-his-side/
It’s legal to kill an enemy in combat, and Soleimani was clearly escalating his attacks on U.S. forces.
In ordering a strike on Iranian general Qasem Soleimani, President Donald Trump re-opened questions about targeting those abroad who would harm Americans. “No one should shed a tear,” in Senator Chuck Schumer’s words, over the death of the Qods Force leader, who was responsible for the killing of hundreds of American soldiers in Iraq. Nevertheless, critics worry that the killing of Soleimani, one of the military leaders closest to Iran’s religious leaders, could spark an escalatory spiral of attacks and lead to a broader war in the Middle East.
Putting aside the policy of the attacks, Trump critics have raised doubts about the legality of the strike. Shortly after news broke on Thursday night of the attack, Senator Chris Murphy (D., Conn.), while conceding that Soleimani was “an enemy of the United States,” tweeted: “The question is this — as reports suggest, did America just assassinate, without any congressional authorization, the second most powerful person in Iran, knowingly setting off a potential massive regional war?”
Killing Soleimani without “involving Congress raises serious legal problems and is an affront to Congress’s powers as a coequal branch of government,” said House Foreign Affairs Committee Chairman Eliot L. Engel (D., N.Y.). “The law requires notification so the President can’t plunge the United States into ill-considered wars.”