Mr. Trump said last week that he would "absolutely" impose tariffs on the European Union. The European Union said it would "resolutely respond" if the United States imposed tariffs on the European Union, the latest sign of discontent with President Trump's trade policies, whose effects are spreading around the world. The use of tariffs is "harmful to all parties" and the European Union has expressed regret over Mr. Trump's decision to impose tariffs on Canada, Mexico and China.