At a town hall here on Wednesday, Mrs. Clinton delivered her most damning, direct criticism of Mr. Trump, saying that he traffics “in prejudice and paranoia,” and that his Muslim proposal was “not only shameful, it’s dangerous.”

But Mrs. Clinton also strove to recognize something stirring in the electorate that Mr. Trump had clearly tapped into. “It’s O.K., it’s O.K. to be afraid,” she said. “When bad things happen, it does cause anxiety and fear,” she added. “But then you pull yourself together and, especially, if you want to be a leader of our country, and you say: ‘O.K., what are we going to do about it? How are we going to be prepared?’”…

Bennie Stickley, a 75-year-old in Gilbertville, Iowa, who retired from a John Deere factory, said he was supporting Mrs. Clinton but agrees with Mr. Trump’s proposal to bar Muslims. “I’m for him on that,” he said. “We shouldn’t be letting those people into the country,” he added.

“She’s as amazed as everyone else is” by his staying power, said Edward G. Rendell, a former governor of Pennsylvania, who recently spoke to Mrs. Clinton about Mr. Trump.