The U.S. Constitution gives the power to impose taxes — including tariffs — to Congress. But lawmakers have gradually relinquished power over trade policy to the White House. And Trump has made the most of the power vacuum, raising the average U.S. tariff to more than 18%, highest since 1934, according to the Budget Lab at Yale University.

The U.S. Court of Appeals for the Federal Circuit in Washington, D.C., will consider the legality of "reciprocal" tariffs that Trump imposed on a broad range of U.S. trading partners in April, as well as tariffs imposed in February against China,