Bobby Bank/WireImage/Getty Images

ABC News' Michael Falcone reports:

Donald Trump appears to be giving Mitt Romney a pass for skipping the presidential debate he is moderating on Dec. 27 in Iowa.

"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 in a statement to ABC News on Tuesday. "But I understand why Gov. Romney decided not to do it."

Trump and his aides declined to elaborate on why he was willing to mostly let Romney off the hook for skipping the debate, a collaboration between the conservative website Newsmax.com, ION TV and the American Conservative Union.

In an appearance on Fox News on Tuesday afternoon, Romney was asked about whether he would show up at the Des Moines debate, which is set to take place exactly one week before the Iowa Caucuses.

"No, I'm not participating in that," Romney told Fox's Neil Cavuto, adding that he had spoken personally to Trump to inform him of the decision. "We have two debates in December that I've  agreed to participate in. The rest of the month will be spent campaigning."

A source close to Trump confirmed that the phone call took place and that Romney was seeking to keep the door open to a potential trump endorsement.

So far only two candidates have confirmed their attendance at the debate: Newt Gingrich and Rick Santorum. Ron Paul and Jon Huntsman have both said they will not participate, and other GOP contenders like Michele Bachmann and Rick Perry are still deciding.

Huntsman's spokesman, Tim Miller, mocked the event as "the 'Presidential Apprentice' Debate with The Donald," and Paul's campaign chairman, Jesse Benton, called the choice of Trump as a moderator "wildly inappropriate" and said his presence at the debate will "contribute to an unwanted circus-like atmosphere."

Trump's role at the debate has not only provoked different responses from the candidates, it has also exposed a rift among conservatives. On Tuesday, two key right-leaning organizations,  Americans for Tax Reform and the American Conservative Union, released statements urging the GOP contenders to take part.

"I believe Newsmax and ION will provide this opportunity for us to properly vet the Republican candidates on the issues," the tax reform group's president, Grover Norquist, said in a statement. "I am assured that Donald Trump will be a fair-minded moderator and joined by serious journalists."

The American Conservative Union, meanwhile, announced its co-sponsorship of the debate.

"We strongly encourage all Republican presidential candidates to participate," ACU's President At Cardenas said in a statement. "This will be a serious debate focused on serious issues. Conservatives across the nation will appreciate a debate hosted by a trusted conservative media outlet like Newsmax."

But other conservative figures, including former Bush administration official Karl Rove and conservative commentators Charles Krauthammer and George Will, disagreed/

This week Krauthammer called the debate "a joke," Rove said Trump "could do a lot of damage" to one of the candidates and Will urged the candidates to say, "we're not going to be hijacked and participate in this."

Trump's top political adviser, Michael Cohen, pushed back on that criticism in an interview with ABC News on Tuesday.

"Donald Trump's appeal is vast and includes not only conservatives, but, in essence, anyone who's interested - irrespective of party affiliation - in making America great and respected again," Cohen said. "It is for this reason that conservatives are imploring all the GOP to participate in the Newsmax, Trump-moderated debate. Those that choose not to are making a grave mistake."

The Newsmax debate will be the last of three such sessions in Iowa during the month of December, including an ABC News-Des Moines Register-Iowa Republican Party debate on Dec. 10.