Rick Perry is now the fourth candidate to turn down the invitation to Newsmax’s Donald Trump-moderated debate. Mitt Romney, Jon Huntsman and Ron Paul have also opted out, which leaves just Michele Bachmann, Rick Santorum and Newt Gingrich to duke it out for Trump’s endorsement:

In a statement, Perry’s campaign says the Texas governor told Trump he’ll be busy meeting Iowa voters before the caucuses Jan. 3.

“Traditional retail campaigning in the days and weeks leading up to the Iowa caucus is the Perry campaign’s top priority,” the statement says.

The statement says Perry, one of several candidates to visit Trump at his New York City office, “respects” Trump “and the folks at Newsmax,” the conservative publication hosting the Dec. 27 debate.

While Gingrich and Santorum have already committed themselves to participating, Bachmann still hasn’t made up her mind. And based on her comments earlier today (she told “Fox and Friends” that she’s worried about Trump being a “biased” moderator), it sounds like she’s leaning against it. Perry’s decision might prompt her to reject the invite. But the prospect of having all that additional airtime to attack Gingrich might be too attractive for her to turn down.

Then there’s this strong criticism of the debate from Republican National Committee Chair Reince Priebus today:

Republican National Committee Chairman Reince Priebus spoke out Thursday against an upcoming GOP presidential debate to be moderated by Donald Trump, saying it would be “malpractice” for him as the leader of the party not to think the debate was problematic.

“We appreciate what Mr. Trump has done, but if you’re still talking about potentially running as an independent candidate, I think that’s a problem,” Priebus said on Fox News. “I think that would be malpractice for me as an RNC chairman to not believe that that is an issue.”

Priebus was careful to say the candidates should make up their own minds, but the message from the RNC is clear: the Trump debate is bad for the Republican Party. And it’s hard to fathom why a candidate for the GOP nomination would want to do something that’s viewed as damaging to the Republican Party. If Bachmann does end up turning down the invitation, will it definitively sink the debate? Newsmax wouldn’t seriously go ahead with just a Gingrich-Santorum showdown, would it? The irony of the situation is that Trump was ostensibly brought on to help attract viewers and media attention, but by driving away most of the candidates, he may actually end up doing the exact opposite.