WASHINGTON — “The assault on the American auto industry is over,” President Trump declared last spring in Detroit, promising auto executives that he would throttle back Obama-era regulations on vehicle pollution.

The moment embodied one of Mr. Trump’s main political promises — to promote pro-business policies that unshackle industry and the economy. He has pledged to create an oil and gas boom that will spawn “massive new wealth” and to renegotiate the North American Free Trade Agreement to eliminate “big trade barriers” for American products. His new taxes on metal imports “have already had major, positive effects” on classic Rust Belt industries like steel and aluminum, the White House has said.

Even as the president’s pro-business stance is broadly embraced by the corporate community, in some significant cases the very industries that Mr. Trump has vowed to help say that his proposals will actually hurt them. They also warn that policies designed to aid one group will eat into someone else’s business in ways that policymakers should have anticipated.

“I would like to tell the president, ‘Man, you are messing up our market,’” said Kevin Scott, a soybean farmer in South Dakota and the secretary of the American Soybean Association. The idea of changing Nafta, he said, “gives us a lot of heartburn in farm country.”