Two more Republican candidates -- Michele Bachmann and Rick Perry -- said thanks but no thanks to an invitation to participate in an Iowa debate managed by real estate mogul Donald Trump.
Perry's campaign said he plans to focus his efforts on traditional retail campaigning in the closing weeks. His campaign announced plans for a 44-town bus tour starting next week.
Bachmann, who earlier this week had expressed reservations about Trump's impartiality, officially RSVPd no Thursday.
Conservative media group Newsmax announced last week it had partnered with Ion Television to host a debate, and had chosen Trump as the moderator.
Before the Perry and Bachmann announcements, Trump acknowledged that his role had given candidates pause.
"People are afraid that I'm going to run as an independent candidate and some of the people that are supposed to be in the debate have expressed that. And I don't want to give up that option, because it certainly is an option," he told CNN's Wolf Blitzer.
But he said he was surprised that Romney backed out. And as for Perry and others: "What do they have to lose?"