By ordering last week’s Tomahawk strike on a Syrian airbase, the president usurped Congress’s exclusive power to declare war. He shouldn’t be allowed to get away with it. Make no mistake: President Trump’s airstrikes against Syria were unconstitutional. Military action may well have been justified from a moral standpoint. The Assad regime’s war on its own people and its use of chemical weapons required a response, arguably including a retaliatory strike to deter further such attacks. Inaction, as much as action, has profound human consequences. There is a case to be made that America should have taken military action against...