MARSHALLTOWN, Iowa -- At one town hall after another, congressional Republicans on recess this week have been getting an earful, and now another issue is testing their hearing.

Firing the head of the FBI as the bureau investigates Russian ties to the Trump campaign fired up the crowd at Iowa Congressman Rod Blum's Thursday town hall, reports CBS News correspondent Dean Reynolds.

Rep. Rod Blum at his town hall CBS News

"If Trump was guilty of something, would he fire the FBI director?" Blum asked.

"Yes!" the crowd yelled.

"Because that's a pretty dumb move," Blum said. "I get it. I mean I get it. You hate the president. I get it."

Blum represents a district that twice voted for Barack Obama but turned red in November. In Marshalltown, Blum was repeatedly forced to defend the president.

The crowd at Rep. Rod Blum's town hall CBS News

"You can't be impeached for something that there's no proof of, so far. There's no proof so far of any collusion between the Trump campaign and Russia," he said.

Among Trump supporters here, Maurice McWhirter was not worried that firing the FBI director might impede the bureau's investigation.

"One guy, even if it's the head guy, doesn't make any difference in whether that investigation goes forward or not," he said.

Fellow Trump supporter Veridee Hand was even less concerned.

"If the Russians worked with Trump to get Trump elected, is that troubling to you?" Reynolds asked Hand.

"No," Hand replied.

"Overall, how do you think President Trump is doing?" he asked.

"I think he's doing very well," she responded.

And since the inauguration, that is the answer CBS News has been getting in state after state from the people Mr. Trump calls his base.