WASHINGTON, June 9 -- Having lost at the Supreme Court, the administration that built its economic program on tariffs now has to hand back much of the money it collected under them, and it is fighting to return as little as it can. The United States is staring at a refund bill of around $175 billion after the levies were ruled an abuse of presidential power, one of the most expensive legal defeats a modern White House has handed itself.

The reckoning began in February, when the Supreme Court struck the tariffs down by six votes to three. Writing for the majority, Chief Justice John Roberts held that the 1977 International Emergency Economic Powers Act, the law Trump had used, was meant for responding to specific national emergencies, not...