A splintered conservative vote in the crucial primary state of South Carolina could pave the way for another win by front-runner Mitt Romney, in a contest due to have one fewer candidate after the expected withdrawal of moderate Jon Huntsman.
Polls show Romney, the former Massachusetts governor who struggled to a fourth-place finish in South Carolina during his 2008 White House run, with a lead heading into Saturday's vote. The state has a large population of evangelicals and other conservative Christians, and concerns arose four years ago about his Mormon faith.
But Newt Gingrich, Rick Santorum and Rick Perry all said Romney, after victories in Iowa and New Hampshire, continued to benefit from the fractured Republican field and the failure of social conservatives to fully coalesce around a single alternative.
That has left Romney in control of the race to challenge President Barack Obama, despite a lack of support from conservatives who are put off by Romney's shifting stances on social issues like abortion.
"I think the only way that a Massachusetts moderate can get through South Carolina is if the vote is split," said Gingrich, portraying himself as the only conservative with a "realistic chance" of beating Romney in the first-in-the South contest.
Huntsman will withdraw Monday, campaign manager Matt David told The Associated Press on Sunday. The former Utah governor and ambassador to China will endorse Romney at an event in South Carolina, campaign officials said.
Huntsman placed third in last week's New Hampshire primary despite devoting most of his campaign resources to the state.
His résumé suggested he could be a major contender for the Republican nomination: businessman, diplomat, governor, veteran of four presidential administrations, an expert on China and on foreign trade. But Huntsman, who tried to avoid levelling attacks on opponents and Obama, was routinely at the bottom of national polls, barely registering at two per cent.
The move comes as pressure has been increasing on Perry, the former Texas governor, to leave the race in order to allow South Carolina's influential social conservatives to unify behind either Santorum, a former senator, or Gingrich, the former leader of the House of Representatives.
Gingrich said he would "reassess" his candidacy if he lost in South Carolina and acknowledged that a Romney victory would mean "an enormous advantage going forward."
"If for some reason he's not derailed here and Mitt Romney wins South Carolina … I think it should be over," said the state's senior senator, Republican Lindsey Graham. "I'd hope the party would rally around him if he did, in fact, win South Carolina."
Santorum said South Carolina is "not going to be the final issue" and spoke of the "need to get this eventually down to a conservative alternative" to Romney. The former Pennsylvania senator who won the endorsement of an influential group of social conservatives and evangelical leaders Saturday in Texas.
The candidates faced a packed week of campaign events and nationally televised debates Monday and Thursday. No Republican has won the party's presidential nomination without carrying South Carolina.
Virtual tie in Iowa
Santorum battled Romney to a virtual tie in Iowa before falling to fifth place in New Hampshire. Gingrich and Perry fared poorly in both states. All three have the backing of well-financed independent groups known as super political action committees that can help keep their candidacies afloat with barrages of advertising.
Santorum refused to suggest anyone should drop out of the race as a way to consolidate conservative support behind an anti-Romney candidate. But he said Republicans would have a hard time beating Obama in November if Romney were the nominee. Santorum cited Romney's push for mandatory insurance coverage in Massachusetts, a model for Obama's health care reform program.
Gingrich and Perry used television interviews to focus on Romney's former leadership of the Bain Capital private equity firm. Both defended raising questions about Bain's business practices, saying Romney's tenure would come under relentless assault from Democrats in the general election.