House Democrats, joined by a few Republicans, responded to the killing of Iran’s Maj. Gen. Qasem Soleimani by questioning the president’s authority to order that strike. But the resolution they passed last week makes a mockery of Congress’s own powers. It purportedly “directs the President to terminate the use of United States Armed Forces to engage in hostilities in or against Iran or any part of its government or military” unless Congress authorizes the use of force or an Iranian attack on the U.S. is “imminent.” But it’s styled as a nonbinding resolution. That means it doesn’t need Senate approval, but it also makes...