For months, President Trump and advisers touted tariffs as a cure-all. But before the Supreme Court, the White House’s solicitor general, D. John Sauer, recast them as “regulatory,” with any revenue merely “incidental.” At the White House, Mr. Trump warned that an adverse ruling would be “devastating,” said he is weighing contingency plans, and claimed trillions in investments from Japan, South Korea and the European Union could be at risk without tariff threats. The case tests whether he exceeded his authority; the administration calls tariffs a foreign policy tool for national security and economic emergencies.

Prepared by Lauren Mitchell and reviewed by editorial team.