Here's a key fact -- perhaps the key fact -- to know as Republicans enter their critical and potentially decisive run up to South Carolina's "First in the South" primary on Saturday: Since 1980, when Ronald Reagan supporters invented the primary there, South Carolina voters have picked the eventual winner of the GOP nomination every time. For that matter, they've picked the Democratic nominee every time but once, in 2004, when they remained loyal to South Carolina native John Edwards.
South Carolina is the home of anti-federal sentiment going back to the 1820s, and the birthplace of the modern, Southern-based GOP thanks to figures like Strom Thurmond, Roger Milliken and Lee Atwater.
The state is to modern Republicanism what Mecca is to Islam: a holy place of its founding history, feuds, orthodoxy and authority.
Before 1980, South Carolina had selected its delegates by convention, a suitably elitist and tightly controlled situation for local Republicans. But seeking an early boost in what had become a Southern-based party, Reagan operatives and loyalists engineered the switch to a primary system. Reagan won in 1980 and was on his way to the White House.
A win now by Romney -- a Yankee, a relative moderate, an Ivy Leaguer and a Mormon -- would be the ratification he desperately needs from voters who, so far, still regard him with mere tolerance at best and deep antagonism and suspicion at worst.
To be sure, Romney can still slog on to the nomination if he loses South Carolina. The Florida primary, 10 days later, is a mega-state event in which only he and Ron Paul have the in-house resources to compete.
But losing the Palmetto State, given its history and what is likely to be a big turnout, would reinforce a narrative Romney can ill-afford: that he's a likely nominee by default, resented and unloved.
"South Carolina is the rubber match and always is," said Charlie Black, a Romney adviser and one of the original architects of the primary. "The voters there are not all evangelicals, by the way. The voters tend to pick the mainstream conservative over the insurgent."
That's true: the South Carolina primary did no endorse Pat Buchanan, Pat Robertson or John McCain in his 2000 outsider bid.
With Jon Huntsman out of the race and endorsing him, Romney has a chance to slip past what remains a divided insurgent conservative opposition.
Romney campaign insiders claim to be more worried about a last-minute surge by Rick Santorum, who won the endorsement of key evangelicals over the weekend, than about Newt Gingrich, who is currently running in second place in the composite polls.
"I'd watch Santorum," Black said.
If Romney wins, it's likely to be with less than one-third of the vote -- hardly a ringing endorsement. Nationally, his numbers are rising quickly, but he still wins the support of barely a third of registered Republicans, and in polls as recently as last week, 58 percent of GOP voters said that they wished other candidates were in the race.
But there aren't. Mitt Romney is available -- which, once again, may be just good enough.