Olu Sonola, the head of U.S. economic research at Fitch Ratings, said the economy was just “starting to see” the effects of the tariffs that Mr. Trump announced in the spring, adding that with Mr. Trump’s newest duties now in place, Americans would “see that magnified” in coming months.

The U.S. has begun officially levying higher taxes on imports from dozens of countries Thursday, four months after President Donald Trump first announced plans to impose tariffs on most of the world w