Sweeping tariffs imposed by President Trump threatened economic upheaval for consumers and businesses in the United States on Tuesday as the country’s biggest trading partners struck back on Tuesday, raising fears of a burgeoning trade war.

       Canada and China swiftly condemned the U.S. tariffs and announced retaliatory tariffs against American exports. President Claudia Sheinbaum of Mexico said that if the U.S. tariffs were still in place on Sunday, she, too, would announce countermeasures.

       “This is a time to hit back hard and to demonstrate that a fight with Canada will have no winners,” Prime Minister Justin Trudeau of Canada said in a stern and, at times, biting address on Tuesday.

       The U.S. tariffs were a stark turnabout from the free-trade evangelism that has marked much of postwar American foreign policy. The measures amounted to 25 percent tariffs on all imports from Canada and Mexico and a 10 percent tariff on all imports from China. They came on top of a 10 percent tariff on Chinese goods put into effect one month ago and a variety of older levies, including those that remain from the China trade war during Mr. Trump’s first term.

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       Amid the tariff dispute, the niceties and flattery that some foreign leaders had employed in the first weeks of the Trump administration seemed to fall away.

       Addressing Mr. Trump as “Donald,” Mr. Trudeau said at a news conference in Ottawa: “You’re a very smart guy. But this is a very dumb thing to do.”

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