Michele Bachmann and Rick Perry have turned down invitations to Donald Trump's much-hyped Republican debate, leaving The Donald with just two attendees: Newt Gingrich and Rick Santorum.

Bachmann told Fox News on Thursday that she was uncomfortable participating in a debate moderated by someone who has said publicly which candidates he prefers.

It suggests the idea of bias, and I just don't know if that's necessarily the right format, she said.

Perry's spokesman, Ray Sullivan, did not mention Trump in rejecting the invitation, saying simply that Perry would be focusing on traditional retail campaigning, not debates, in the short time remaining before the Iowa caucuses on Jan. 3.

Will Trump-Moderated Debate Take Place?

While Bachmann's and Perry's rejections were more diplomatic than those from Ron Paul and Jon Huntsman, there is no getting around the result: if Trump goes forward with the debate, he will be moderating an almost empty stage.

When Paul and Huntsman turned down Trump's invitation last week, Trump dismissed them as joke candidates and said he was glad they weren't coming because they would be wasting the time of the viewers who are trying very hard to make a very important decision -- even though Paul is tied with Mitt Romney for second place in Iowa.

But then Romney, who has praised Trump in the past, announced that he, too, would be skipping the debate. And with Bachmann's and Perry's decisions to do the same, Trump is left with naught but Gingrich and Santorum, who, with just 4 percent support in national polls, is a joke candidate if ever there was one.

It seems that -- despite the insults Trump has hurled at candidates who criticized him, and despite the mocking from Gingrich, who said, You want me to believe you can debate Barack Obama but you're afraid to show up with Donald Trump? -- most candidates have heeded the advice of people like Republican National Committee Chairman Reince Priebus, who noted the conflict inherent in having a debate moderated by someone who is still talking about running as an independent.

There is also the small fact that, according to an NBC poll, voters say by a 2-to-1 margin that they would be less likely to vote for a candidate endorsed by Trump. Candidates, especially those who are running behind, have little to gain by associating with someone so clearly unpopular.

Trump's press office did not immediately respond to a request for comment Friday morning, and he has given no indication so far of whether he will cancel the debate or move forward with such dismal participation.