Lots of Republicans will be watching tonight's debate carefully. If Romney cannot fend off a challenge from a manifestly flawed candidate like Gingrich, then he's toast when he comes up against the President's slick political machine.
Romney doesn't have to out-Gingrich Gingrich tonight. But he does have to show resilience, the ability to learn (McCain's 2008 campaign manager once described him as a "learning organism" -- we'll see if he's right), the heart to come out fighting, and the capacity to make a case for himself in a way that allows him to connect, at least to some degree.
His success or failure may determine whether South Carolina is a blip or the beginning of a long slide that spells danger for the GOP's chances next November.