MEXICO CITY — Mexico’s president responded angrily Tuesday to President-elect Donald Trump’s pledge to impose a 25 percent tariff on its products if the country didn’t curb the flow of irregular migrants and fentanyl, warning that the penalties would only wind up causing inflation and unemployment in the United States.

President-elect Donald Trump announced Monday he plans to impose a 25% tariff on all products coming into the U.S. from Mexico and Canada as one of his first acts back in the White House. On the campaign trail, Trump frequently touted tariffs as a way ...