Nearly four weeks into a costly global trade war with no end in sight, Mr. Trump is facing a barrage of lawsuits from state officials, small businesses and even once-allied political groups, all contending that the president cannot sidestep Congress and tax virtually any import at levels to his liking.

Small businesses will have no choice but to raise prices, cut staff, delay growth plans or shut down entirely just to keep up with the rising costs of imports they can’t source domestically, one expert said.

During a press gaggle on Air Force One, President Trump was asked what it would take for him to reduce tariffs on China.