Mr. Vilsack said that Republican-leaning institutions like evangelical churches and the National Rifle Association had been far more effective at building coalitions than Democratic groups. “Evangelical churches and the N.R.A. are about community, getting the message out and supporting each other,” he said.

To win back voters, Mr. Vilsack said, Democrats need to counter Republicans’ mantra that the federal government is rife with “fraud, waste and abuse,” by conveying that it is part of the solution, not the cause of all problems, and that it can be an engine for economic growth.

“We don’t sell government, nothing pushing back against the message that government doesn’t work,” Mr. Vilsack said.

He said he was having success persuading Democrats to change their ways, an assertion that will be tested in the governor’s race next year. And not everyone is convinced that the Republican ascendancy is permanent.

Timothy Hagle, a professor of political science at the University of Iowa who has written extensively about Iowa voting behavior, said that Mr. Trump’s election did not necessarily signal a fundamental shift to Republican territory, and that the election may have turned more specifically on the candidates and issues.

Many Republicans agree that they cannot take their newfound fortune for granted.

“Republicans in Iowa feel good about our circumstances, but we always know things can change very quickly,” said Tim Albrecht, a senior adviser to Gov. Kim Reynolds.