President Trump appears to be testing the American political system’s tolerance for soft dictatorship through the cavalier—and potentially illegal—use of presidential emergency powers. On February 15, after months of blustery threats, he declared a national emergency on the southern US border and dispatched the Army Corps of Engineers to administer the construction of a wall by private contractors in order to stop the flow of migrants and drugs into the country from Mexico. Trump issued the executive order because after a thirty-five-day government shutdown over funding for the border wall, Congress had just passed a spending bill that included only a fraction—$1.375 billion—of the $5.7 billion he wanted for the wall and specified that it be constructed of fencing rather than the steel he had demanded. The House and Senate passed a joint resolution to terminate the national emergency declaration, which Trump vetoed. The House was then unable to muster the two-thirds majority required to override the veto.

Legislators have good reason to oppose the construction of a border wall. Trump’s arguments for building one—mainly that illegal immigration is rampant, that illegal immigrants commit more crimes than US citizens, and that the bulk of illicit drugs enter the United States through illegal border crossings—are demonstrably false. Trump himself betrayed his own claims of urgency when he said, in declaring the emergency, “I didn’t need to do this, but I’d rather do it much faster.”

Over strong objections from the House Armed Services Committee, the Defense Department has begun to divert $4.3 billion for the wall from about 150 military construction projects—many of them urgent and long delayed—including a new school and a water treatment facility on stateside military bases and a new National Guard fire station. More US troops are likely to join the three thousand active-duty soldiers and two thousand National Guard members currently deployed at the border. And because the Department of Homeland Security does not have enough facilities in which it can house and oversee all the migrants it has detained, it wants the Pentagon to set up additional ones on US military bases, although some senior Pentagon officials reportedly consider it inappropriate to use the military to handle a civilian issue like immigration.

Congress has delegated to the president broad authority to invoke a national emergency, presidents have done it dozens of times, and the courts have shown little appetite for questioning the president’s emergency powers.1 But the legal, political, and factual background to Trump’s declaration illuminates its egregiousness. The International Emergency Economic Powers Act, enacted in 1977, has been the basis for about 80 percent of the emergency powers that presidents have exercised. It was designed specifically to allow the president…