DES MOINES — Hoarse and on the verge of losing his voice, Republican presidential candidate Jeb Bush on Wednesday mocked Donald Trump's plans to skip a Thursday night debate here, saying it proves again that he's unfit to be the party's nominee.

"He thinks he’s not being treated fairly. Really? Donald Trump’s not being treated fairly by the press? He consumes all the press! He’s a Stradivarius violinist from the Vienna Symphony" who plays the press, Bush said in response to a voter's question.

"Poor little Donald, being mistreated. If you think he’s going to be mistreated now? ... How do you think the general election’s going to work out?" he added. "Or dealing with [Russian President Vladimir] Putin? Or dealing with the challenges of being president? That notion just doesn’t pass muster."

Bush fielded questions Wednesday afternoon from a few hundred employees of Nationwide Insurance, which has hosted presidential candidates at its downtown headquarters here since 1980.

Coughing and sipping from a water bottle throughout the event, Bush warned the group that "I’m losing my voice, which is not a good sign four days before the Iowa caucuses." But the question about Trump from a man in the crowd seemed to buoy him a bit.

He reminded the crowd that Trump has made insulting comments about women, prisoners of war and disabled people.

"It’s not a sign of strength. That’s just weird," he said. "My case against Trump is a case to protect the conservative cause, because I live it, I love it, I believe in it."

Bush isn't much of a factor in the Iowa caucuses, where Trump and Sens. Ted Cruz (Tex.) and Marco Rubio (Fla.) are leading the GOP pack. But he has been the most vocal critic of the Republican front-runner, and he faulted his other opponents for being in the "witness protection program" and not confronting Trump more often.

"This goes beyond my campaign, I don’t know if it’s good for me or bad for me, I know everyone else seems to be in the witness protection program," Bush said.

The former Florida governor appeared to concede his underdog position a few times during the event. One woman began a question to him by saying that she'd seen him in one of the recent debates.

"Which one?" he asked. "They’ve all been doozies."

Bush told reporters as he left the event that he has a $20 bet with aides that Trump will show up Thursday.

"It's in his interest," he said.