For months President Donald Trump has been slapping higher tariffs on practically every country’s exports to the United States, citing emergency economic powers.

U.S. appeals court judges sharply questioned on Thursday whether President Donald Trump's tariffs were justified by the president's emergency powers, as lawyers for states and businesses challenging the measures argued he exceeded his authority.

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.