Michele Bachmann is not participating in Donald Trump's NewsMax debate in Iowa, her spokesman said Thursday.

Bachmann is the final GOP contender to RSVP, and in doing so joins a long list of candidates -- Rick Perry, Mitt Romney, Ron Paul and Jon Huntsman -- who have declined the invitation.

Only Newt Gingrich and Rick Santorum have agreed to participate in the Des Moines debate.

The Minnesota congresswoman has visited the reality television celebrity four times at his Trump Tower office.

But a week ago when the announcement of the Dec. 27 debate was made, Trump openly speculated about what would happen to Bachmann's supporters if she dropped out of the field.

"If Herman goes or if Michele goes or if somebody goes, he doesn't seem to pick up those poll numbers," Trump said of Romney in a phone interview with Special Report anchor Bret Baier.

Fox News producer Jake Gibson contributed to this report.