The Supreme Court is poised to decide a potentially momentous question for U.S. democracy: can the president unilaterally deploy federal troops on U.S. soil over the objections of state governors? In Trump v. Illinois, the Supreme Court will soon decide whether to issue a stay of a district court’s injunction of the deployment of National Guard troops to Chicago. The government’s brief argues there is “no reason to believe that courts can, or should, second guess the President’s conclusion” that military force is needed to suppress an emergency. “[T]his case,” the brief argues, falls in the heartland of unreviewable presidential...