Trading partners might not make good on their commitments, tariffs could drive up inflation and stymie growth, and courts could rule against the president’s ad hoc levies.

Many smaller countries’ exports have faced 10 percent tariffs since the president first announced, then suspended, an initial wave of policies in April. Others have staved off eye-watering rates after brokering deals with the United States that set their tariffs generally between 15 and 20 percent.

When President Trump rocked the economy with an unprecedented attack on global trade in April, the plan was dismissed as swaggering, capricious and unsustainable.