Philip Klein hypothesizes

It's true that there are states in which Rick Santorum and Newt Gingrich can theoretically beat Romney, but if they can't beat him in South Carolina, where will they go from there? Even now, Romney has a 23-point lead nationally, according to Gallup. Sure, perhaps Rep. Ron Paul's fervent supporters can out-hustle Romney's organization in a caucus here or there. But it's also possible that Romney will run the table. Remember, as the field gets narrowed, it'll get a lot harder for Paul to outright win a state, because he'll have to start getting into the 40-50-plus point range. Romney may have had a lot of vulnerabilities going into the GOP nomination battle, but he continues to benefit from weak competition.