“I think the president has done a lot of really good things for the economy,” he said. “We’ve seen growth and jobs and wages all moving in the right direction. And I don’t know why we would want to step on that.”

Economists say the tariffs already amount to a significant tax increase on Americans, by raising the prices of goods they buy, according to new studies from the Tax Foundation in Washington and the Penn Wharton Budget Model at the University of Pennsylvania. The damage is concentrated, as a percent of income, at the lowest rungs of American income earners, who spend a larger share of their salaries on imports than the upper middle class and the rich.

Additional tariffs on Mexico and China would wipe out all or most of the benefits his 2017 tax cuts delivered to low- and middle-income Americans, the analyses found.

Higher-income Americans would still be net winners from Mr. Trump’s tax and tariff policies, but their benefits would be diminished as well.

“Once you start adding in the tariffs and start talking about what Trump wants to do at the end of the day,” said Kyle Pomerleau, the chief economist at the Tax Foundation, which produced its analysis at the request of The New York Times, “it gets harder and harder for Trump and Republicans to claim that they are cutting taxes for the middle class.”

The Tax Foundation projected widespread benefits from the Trump tax cuts, with the largest gains, in dollar terms and as a share of income, concentrated among high earners. Its new analysis, of the distributional effects of Mr. Trump’s imposed and threatened tariffs, finds widespread harm to Americans, who would pay higher prices on imported goods.

Accounting for both the tax cuts and the full range of tariffs, the Tax Foundation estimates, the lowest-earning fifth of American taxpayers would see an effective tax increase of 1.1 percent of their income this year. Those in the middle fifth would see a 0.3 percent tax increase. Upper-middle-class earners would have their gains from tax cuts wiped out. Only the top 5 percent of earners would continue to see a net tax cut of more than 1 percent on the year.