Rep. Ron Paul says he will not take part in a December GOP Debate in Iowa and it is because of the choice of moderator. It seems Paul hasn’t forgiven Donald Trump for backing out of a keynote speech at a fundraising dinner hosted by the Manhattan County GOP in Iowa earlier this year. Gov. Rick Perry ultimately took his place.

In an email statement sent Saturday, Paul’s campaign called Trump’s selection “wildly inappropriate because of his record of toying with the serious decision of whether to compete for our nation’s highest office, a decision he appeared to make frivolously.” Spokesman Gary Howard blamed Trump for costing the Republican Party of Iowa fundraising money and causing embarrassment when it had to offer refunds.

The Paul campaign is also questioning the legitimacy of the debate. In his statement, Howard said, “Mr. Trump’s participation as moderator will distract from questions and answers concerning important issues such as the national economy, crushing federal government debt, the role of the federal government, foreign policy, and the like. To be sure, Mr. Trump’s participation will contribute to an unwanted circus-like atmosphere.”

Trump responded to Paul’s comments with a jab of his own. He told CNN “As I said in the past and will reiterate again, Ron Paul has a zero chance of winning either the nomination or the Presidency. My poll numbers were substantially higher than any of his poll numbers, at any time, and when I decided not to run, due to the equal time provisions concerning my hit show The Apprentice, I was leading the Republican field."

Candidate Jon Huntsman also declined the invitation because of Trump’s participation. In an email to Business Insider, Huntsman campaign spokesman Tim Miller didn’t hide his disdain, saying “Lol. We look forward to watching Mitt and Newt suck-up to The Donald with a big bowl of popcorn,"

Former Massachusetts Governor Mitt Romney was non-committal when asked if he would attend, saying there were more than a dozen debates scheduled, and he hadn’t made a decision yet.