Welcome to the most important week of the 2012 Republican presidential race. Over the next five days, there will be two debates — one Monday, one Thursday — and then, on Saturday, the South Carolina primary.

If there was ever a week when Mitt Romney’s momentum could be slowed, it’s this one. South Carolina, with its active evangelical community and conservative electorate, is the toughest sell for the former Massachusetts governor who has won the Iowa caucuses and the New Hampshire primary already this year.

Should Romney survive the two debates and then claim victory in South Carolina on Saturday, the nomination fight will be effectively over just 18 days after it began.

At the moment, that seems to be the most likely outcome. “The truth is, with each passing day, it doesn’t look likely that anyone can beat him,” said Sally Bradshaw, a former chief of staff to former Florida governor Jeb Bush. “If Romney wins South Carolina, it is over.”

The problem for the not-Romneys is threefold. One, he has proved to be the most disciplined and best debater in the field. Two, conservatives seem to remain unsure of whether they should rally behind an alternative to keep Romney from the nomination — and if so, which one? Three, the anti-Romneys can’t seem to settle on a winning message against him.

With the exception of his hard-to-explain decision to bet Texas Gov. Rick Perry $10,000 during a debate late last year, Romney has been almost entirely unflappable in more than a dozen debates to date. He has stayed entirely focused on President Obama and the economy, rarely diverting from that message to pay attention to anyone on the debate stage unless directly attacked.

And his opponents have largely played along. Unlike in 2008, when Democratic candidates routinely ganged up on the then-front-runner, Sen. Hillary Rodham Clinton, in a series of debates, the GOP field this time around seems far less willing to team up against Romney.

Even when two or more of the candidates do attack Romney, the results aren’t always beneficial to them. The double-barreled attack on Romney’s work at Bain Capital by Gingrich and Perry, who has described what Romney did as “vulture capitalism,” appear to have backfired.

“Gingrich and Perry may have delivered the nomination to Romney by highlighting his private-sector experience in a way that diminished both their candidacies,” said Jim Dyke, a Republican strategist based in South Carolina. “Romney seems to be rallying South Carolina fiscal conservatives, and no other candidate seems to have a plan to deal with it.”

The unwillingness (or inability) of his opponents to put a negative focus on Romney is the broader story of the South Carolina primary. While Romney is the lone serious candidate competing for the establishment/electability-
over-all wing of the state’s GOP, Gingrich, Perry, former senator Rick Santorum (Pa.) and, to an extent, Rep. Ron Paul (Tex.) are all trying to emerge as the candidate of social conservatives and the tea party.

Santorum got something of a boost over the weekend when a group of social conservatives huddled in Texas and decided to back him. But the evangelical leaders said they had no plans to call for any of the other candidates — Gingrich, Perry — to drop from the race, making their endorsement decidedly symbolic. (In a further sign of the inability of social conservatives to rally behind a candidate, forces aligned with Gingrich insisted the group was far more internally divided than the Santorum endorsement indicated.)

Polling makes the problem plain. Romney seems to be capped somewhere in the low 30s in surveys of the South Carolina electorate. But Gingrich and Santorum are splitting up another 40-plus percent of the vote evenly enough that Romney is still the clear leader. (Interestingly, most data in South Carolina suggest that it is Gingrich, not Santorum, who is the more viable anti-Romney in the state.)

“I think the only way that a Massachusetts moderate can get through South Carolina is if the vote is split,” Gingrich said on NBC’s “Meet the Press” on Sunday. “But we have six days to make our case to people.”

Alex Castellanos, a Republican media consultant who worked with Romney in his 2008 presidential race but is neutral in this contest, thinks it’s already too late for the non-Romneys — no matter what happens in South Carolina on Saturday.

“Somebody already has emerged as the anti-Romney: Romney,” Castellanos said. “When Newt attacked him from the left [on Bain Capital], it made Romney the candidate of the right. Romney got more conservative votes than anybody in New Hampshire. Win or lose in South Carolina, he’s it.”

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