President Trump has raised or lowered tariffs/taxes, or he has threatened other nations that he will do so, on an almost daily basis since Inauguration Day. He does not have the legal authority to do so.
The U.S. Constitution authorizes the imposition of tariffs in the very first clause of Article I, Section 8, which famously grants Congress eighteen, and only eighteen, limited and enumerated legislative powers. That Clause provides that:
The Congress shall have Power To lay and collect Taxes, Duties, Imposts and Excises, to pay the Debts and provide for the common Defence and general Welfare of the United States; but all Duties, Imposts and Excises shall be uniform throughout the United States.
