Mr. Trump’s decision to impose tariffs on metals is not new. In his first term, the president levied tariffs on foreign steel and aluminum globally, angering allies like Mexico, Canada and the European Union. He ultimately rolled back some of those barriers on Canada and Mexico when they signed a revised trade agreement with the United States.

The president, who has threatened and delayed other tariffs, said he will announce the measures Monday. Canada and Mexico are among the top U.S. steel suppliers.

“Any steel coming into the United States is going to have a 25% tariff,” he told reporters Sunday on Air Force One as he flew from Florida to New Orleans to attend the Super Bowl. When asked about aluminum, he responded, “aluminum, too” will be subject to the trade penalties.