Fox News anchors Chris Wallace, Megyn Kelly and Bret Baier are all expected to assume their positions as co-moderators at Thursday's Republican presidential debate in Iowa, even as GOP front-runner Donald Trump has held his ground that he will not appear on the Des Moines stage if Kelly is asking the questions. Trump has insisted that he will not subject himself to what he says was an "unfair" line of questioning from Kelly during the first GOP primary debate, which Fox News also hosted.

“Megyn Kelly’s really biased against me,” Trump said in an Instagram video posted Tuesday. “She knows that. I know that. Everybody knows that. Do you really think that she can be fair at a debate?”

Wallace, Kelley and Baier's moderating of the showdown is expected to feature a combination of their own questions as well as those from the audience.

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Kelly, who is the network's “The Kelly File” host, gained during the previous presidential election after she confronted Republican strategist Karl Rove over his refusal to acknowledge Barack Obama had won the 2012 election. She responded to Trump's decision Tuesday night on her show.

"What's interesting is here is Trump is not used to not controlling things as the chief executive of a large organization," Kelly said. "But the truth is, he doesn't get to control the media, and while he's made his position clear about me after that first debate. Roger Ailes made his position clear too. And you know when Trump started it up again this past Saturday and resumed it again and again and again, he was told repeatedly our debate team is settled and then came that Instagram video he put out today, followed by the company's statements."

Wallace, 67, has covered U.S. elections since working at Fox News beginning in 2003, and Baier, 45, is the news station's chief political correspondent.

While Trump will likely not appear on stage, the following candidates have been invited to attend: Texas Sen. Ted Cruz, Florida Sen. Marco Rubio, retired neurosurgeon Dr. Ben Carson, former Florida Gov. Jeb Bush, New Jersey Gov. Chris Christie, Ohio Gov. John Kasich and Kentucky Sen. Rand Paul.

Former Hewlett-Packard CEO Carly Fiorina, former Arkansas Gov. Mike Huckabee, former Pennsylvania Sen. Rick Santorum and former Virginia Gov. Jim Gilmore were invited to the so-called undercard debate at 7 p.m. for lower-popular candidates.

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The prime-time showdown will air at 9 p.m. Thursday EST on Fox News Channel.