Donald Trump's GOP Debate: Mitt Romney Becomes Third Candidate Who Won't Participate

Former Massachusetts Gov. Mitt Romney on Tuesday became the latest Republican presidential candidate to say he will not participate in the upcoming debate moderated by Donald Trump.

Romney told Fox News' Neil Cavuto that he called Trump and told him he would not attend because he was too busy to appear at Dec. 27 forum in Des Moines, Iowa.

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“No, I’m not participating in that,” Romney said. “We have two debates in December that I’ve agreed to participate in. The rest of the month will be spent campaigning.”

For his part, Trump told ABC News in a statement that he accepted Romney's decision.

“It would seem logical to me that if I was substantially behind in the polls, especially in Iowa, South Carolina and Florida, I would want to participate in this debate,” Trump said. “But I understand why Gov. Romney decided not to do it.”

Several prominent Republicans have urged candidates to skip the debate, according to the Associated Press. They predict it will be a media circus and a distraction from important issues.

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So far, two candidates have declined to appear -- Texas Rep. Ron Paul and former Utah Gov. Jon Huntsman -- the latter of whom to'd CNBC's Larry Kudlow that he believes the debate is just a publicity stunt.

"This isn't about ratings for Donald Trump; this is about jobs for the American people," Huntsman said.

Former House Speaker Newt Gingrich and former Pennsylvania Sen. Rick Santorum are the only two candidates to confirm their participation in the debate so far, with other candidates including Minnesota Rep. Michele Bachmann and Texas Gov. Rick Perry yet to make an announcement. However, Bachmann on CBS' Early Show expressed concerns about Trump's objectivity, saying "he said he's already learning towards a candidate."

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Trump made headlines earlier this year when he suggested that President Barack Obama is foreign-born while saying that he might run for president himself. In May, he announced he would not be running, saying: "Business is my greatest passion, and I am not ready to leave the private sector."

Still, he has not ruled out a presidential bid as a third-party candidate.

The Dec. 27 debate is scheduled to air on Ion.