“While it seems that the tariff issue is reopening a fundamental schism between Trump and old-line Republicans, the average-guy voter Trump seems to aim at and do rather well with seems as happy as a clam with the tariffs,” said Clyde Prestowitz, the author of “The Betrayal of American Prosperity.” “I guess my question is: Does Trump have a problem, or do the old-line Republicans who seem to be retiring at a rapid rate have a problem?”

While Mr. Trump’s views on many issues have been flexible or evolved over the years, his belief that the United States was being shafted has been a core conviction going back decades, long before he first ran for president. It is an article of faith that has informed his opinion of trade pacts, tariffs and manufacturing and that helped him tap into populist discontent during the presidential campaign in 2016, particularly in traditionally Democratic states in the Midwest like Wisconsin, Michigan and Pennsylvania.

“I was elected, at least partially on this issue,” Mr. Trump said on Tuesday. “And I’ve been saying it for 25 years: Our country’s been taken advantage of by everybody, by everybody — almost everybody. And we cannot let that happen any longer — not for our companies and not, most importantly, for our workers. So we’re not going to let it happen.”

The disagreement on trade was obscured through much of Mr. Trump’s tenure because he talked more about the issue than took action on it, meaning Republican free-traders could turn aside for a time.

He pulled out of the Trans-Pacific Partnership, a 12-nation trade deal negotiated by President Barack Obama, but the agreement had never been ratified by Congress and seemed unlikely to be. Mr. Trump threatened to scrap the North American Free Trade Agreement with Mexico and Canada, but backed off in favor of negotiations that so far have not yielded consensus. He has likewise suggested he would withdraw from a trade deal with South Korea but has not followed through.