WASHINGTON, DC, United States (AP) — The Republican Party’s steadily rightward drift, exemplified by the tea party movement’s muscle, keeps hitting a quadrennial paradox that frustrates social conservatives: presidential primaries.

For all its success in congressional races, the Republican Party’s right wing repeatedly has failed to unite behind a “movement conservative’’ to be the party’s White House nominee. It happened in 2008 with John McCain, and in 1996 with Bob Dole.

Now social conservatives fear it’s happening again in, of all places, South Carolina, virtually the heartland of the tea party which advocates limited government, deep government spending cuts, and lower taxes. Former Massachusetts Gov. Mitt Romney is running strong in polls there, threatening to sweep the year’s first three Republican contests and all but lock up the nomination in Saturday’s primary.

More than 100 evangelical and social conservative leaders convened last weekend in Texas, hoping to slow Romney’s march by backing former Sen. Rick Santorum. But they were far from unanimous, and many party activists feel the effort was too puny and too late.

The loose-knit group’s lack of cohesion – underscored Monday when some members announced their strong support for former House Speaker Newt Gingrich – illustrates the hard right’s historic difficulty in coalescing early behind one strong contender.

Romney, meanwhile, caught a break Monday. Former Utah Gov. Jon Huntsman, widely seen as competing with Romney for moderate-conservatives’ votes, dropped out and endorsed the front-runner.

Romney began the contest as the Republican establishment’s favorite, running a steady but unspectacular campaign while rivals on his right soared and crashed. Rep. Michele Bachmann and businessman Herman Cain eventually dropped out. Former Alaska Gov. Sarah Palin never got in. Gingrich and Texas Gov. Rick Perry are hanging on, but they have fallen dramatically from their respective high points of last year.

Santorum, virtually an afterthought in the race until Christmas, may have the best chance of becoming the non-Romney candidate. But he lags far behind Romney in money, organization, and experience.

There are several explanations, perhaps none of which will satisfy people who want an unabashed, staunch social and fiscal conservative as president.

The most benign explanation is that Republicans are so intent on ousting President Barack Obama that they will settle for a far-from-pure conservative nominee and rally around him this fall. Indeed, Republican polls show Romney’s perceived “electability’’ as one of his greatest assets.

Tony Perkins, who attended the Texas gathering as head of the conservative Family Research Council, says social conservatism is “choking on its own success’’ by attracting so many presidential hopefuls.

“The field is so inviting for socially conservative candidates to get in,’’ Perkins said, “they slice up the vote.’’

But Dan Schnur, a former campaign and policy adviser for Republicans, says conservative activists keep getting outmaneuvered by the party’s more pragmatic and mainstream operatives who know how to run campaigns.

Among national Republicans, “a balance of power has shifted from the establishment to the grassroots,’’ said Schnur, who teaches politics at the University of Southern California. “That said, the thing about establishments is: They are established, and they are organized.’’

Social conservative crusader Pat Buchanan and business publisher Steve Forbes ran in 1996, but the establishment backed Dole, a longtime Senate leader and an uninspiring campaigner.

In 2008, many on the Republican right disliked McCain, the Arizona senator who championed campaign finance limits and thumbed his nose at other conservative orthodoxies. But he easily passed Baptist minister and former Arkansas Gov. Mike Huckabee, who won the 2008 leadoff Iowa caucuses.