Having already won Iowa and New Hampshire -- becoming the first Republican candidate since President Gerald Ford to do so -- Mitt Romney now finds himself gaining a comfortable lead in South Carolina. Sure, a lot can happen between now and Saturday's primary. Current polling doesn't reflect any bounce Rick Santorum may get from the endorsement of Christian conservative leaders, it's still unclear whether attacks on Romney's record at Bain Capital will have an effect and there are two debates this week. But let's say that Romney does win in South Carolina. Is there anything stopping him from sweeping all 50 states?

Think about it. Romney has a commanding lead in Florida, and will simply obliterate the field if he enters the Sunshine State after having won South Carolina. And if he does win South Carolina and Florida, what will become of the rest of the field? Rick Perry, who came in fifth in Iowa and bailed on New Hamphshire, already has very little justification for continuing. A distant finish in South Carolina would give him even less reason. 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.

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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. And that may allow him to pull off what might have been unthinkable even a few weeks ago -- a clean sweep of every primary contest.