President Trump may not be terminating the North American Free Trade Agreement, known as Nafta, but that doesn’t mean the deal is safe.

After telephone calls with President Enrique Peña Nieto of Mexico and Prime Minister Justin Trudeau of Canada in late April, Mr. Trump said he would start the process of renegotiating Nafta, a treaty that he had scorned during his presidential campaign, calling it “the single worst trade deal” ever signed by the United States.

Whatever his criticisms, Nafta has had a major impact on the American economy in the decades since it was signed, and any renegotiation would affect certain industries.