And even before the Santorum endorsement, whose value at this late hour is questionable, some GOP strategists in South Carolina were counseling caution in predicting the outcome next Saturday.
"It's too early to give [Romney] the crown," says J. David Woodard, a political scientist at Clemson University in Clemson, S.C. and a Republican consultant. "Just because he came in here with some momentum doesn't mean it's over."
After all, Romney came in fourth in South Carolina in 2008 with 15 percent, behind Arizona Sen. John McCain, the eventual GOP nominee, former Arkansas Gov. Mike Huckabee, and former Tennessee Sen. Fred Thompson.
Of course, Romney has the potential to do what Senator McCain did: take advantage of a divided field and win with a modest plurality. McCain won South Carolina four years ago with only 33 percent of the vote. But the state's Republicans are proud hosts of the first primary in a red state, and some don't rule out the possibility that another candidate could stage a late surge and win.
"Romney's a moderate, and we like conservatives," says Mr. Woodard, who is neutral in the primary. "In 2008, McCain remade himself into a more conservative and acceptable person. Now Romney's getting pounded on the radio over his abortion stand. I'm not sure he has the credentials to win conservatives."
And, he adds, there’s a lesson in the nomination of McCain: “We voted for a moderate in ’08 and lost [in the general election].”