Mind you, there are a few things afoot that could affect this Saturday's primary in South Carolina. Such as the fact that everybody else in the field finally realized Romney is about to walk away with it, and targeted him relentlessly in last night's debate. Not to mention which, they are spending heavily in the state with advertising that focuses on him, rather than each other. Santorum certainly got a boost when the evangelical conference this past weekend decided he was their last best hope for a conservative alternative to Romney, and backed him with surprising unanimity. Meanwhile, in the pro-Romeny camp, Hunstman has decided to drop out and back Romney.
The net effect of all of this? Just about nothing. To see why, you have to look no further than the latest Real Clear Politics averages for South Carolina:
Gingrich is not getting any upward trajectory for all his spending, but neither is he dropping. Santorum has similarly plateaued after a weak New Hampshire showing. The state is friendly to them, but they both have limitations in field strength, and are competing with each other for the same votes. Perry is meanwhile making his last stand, but clearly not getting any traction out of it, and any hope he held onto that evangelicals would rally around him is clearly dashed after this weekend. Santorum could get some boost from the evangelical backing, but no recent poll has him closer than 15 points behind Romney, and that's way too much to make up in 5 days, especially with Gingrich and Perry continuing to unroll their remaining advertising riches. And the considerable anti-Romeny advertising money that has been floating around is meanwhile largely focused on attacks on his business record that have actually caused conservatives to come to his defense, rather than on the social issues where he is much more vulnerable.
All of this combines to pretty much hold in place the following math, which you can see above:
Santorum & Paul=14.3% each
Hypothetical united Conservative would win, narrowly, about 41%-37%, but neither Gingrich or Santorum will get that high unless almost all of the other's votes plus Perry's flow to them in the next five days. Which, absent a candidacy-ending scandal, isn't going to happen. Meanwhile, Perry has insisted he'll stay in through Florida, and Santorum and Gingrich have already spent so much money ahead in the state that they'll be heavily tempted to as well no matter how South Carolina turns out. Which makes it very likely that another split field will hand Romney four in a row.