Cain was tied with Romney according to a CBS poll released Friday, with each earning the support of 17 percent of Republican voters. That represented a rise of 12 percentage points for Cain, and a decline of 11 percent for Perry, who nearly halved his support to 12 percent.

Former New Mexico Gov. Gary Johnson, who appeared for the first time at the Fox News debate in Orlando, was not invited to participate in the Washington Post/Bloomberg debate.