Mr. Wagner was unmoved by the Nixonian comparisons drawn by many Democrats. He said that he hadn’t paid much attention to politics during the Watergate era, but that he was dialed in now, adding, “I’d like the truth to come out.”

He said Mr. Trump’s bluster was “scary as hell,” and made him concerned about his children and grandchildren, as well as relatives who are the children of immigrants. He said he would not vote for a liberal Democratic challenger to Mr. Trump, but could support a conservative primary challenger, or even a moderate Democrat.

“I want to get Donny out,” he said. “I wouldn’t mind if he got kicked out tomorrow — he’s that bad. Once was enough.”

Yet Barbara Hames-Bryant, president of a manufactured-home retailer in Marion, Iowa, saw a business owner’s decisiveness at work.

“That’s points for Trump,” she said. “Whether Comey is right or wrong, he handled it quickly.”

On Wednesday Ms. Hames-Bryant sat in her-ground floor office, her desk cluttered with an obituary, a death certificate and other papers from her father, Troy Hames, who died on April 30 at the age of 92. Her father was a strong supporter of the state’s Republican congressional delegation, she said.

She herself was not an early supporter of Mr. Trump, but said she was encouraged by his pro-business posture. Cutting ties with employees or contractors was part of the job, she said, and she gave Mr. Trump credit for what she called an unequivocal break.

“People who don’t run a business don’t understand the reality of those decisions,” she said.