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Charles Dharapak, Associated Press
Republican presidential candidate, former Massachusetts Gov. Mitt Romney, presents a birthday cake to South Carolina Gov. Nikki Haley as he campaigns at Charleston Area Convention Center in North Charleston, S.C., Friday, Jan. 20, 2012. At rear center is Virginia Gov. Bob McDonnell.

CAYCE, S.C. — For weeks, Renee Boling was sure she was going to vote for Mitt Romney in South Carolina's Republican presidential primary. But a series of events this week changed her mind, and seemingly the minds of many others across the state.

Romney repeatedly refused to release his income tax return and was on the defensive in two debates, while Newt Gingrich and Rick Santorum made forceful arguments that led Boling to rethink whether the former Massachusetts governor was really the best candidate the GOP could offer. The 37-year-old administrative assistant said Friday she was leaning toward Santorum, but could change her mind in the hours before she votes.

"He just didn't back down," Boling said of Santorum's performance at Thursday night's debate. "He stood his ground."

The dynamics of South Carolina's campaign have shifted dramatically in the last week after a series of events threw the race into turmoil and left countless voters undecided about who to support. Romney was positioned to win here after his commanding victory in New Hampshire. But polls now show he has slipped from the front of the pack to what he described Friday as a neck-and-neck contest with Gingrich. Santorum and Texas Rep. Ron Paul trail in surveys.

The chaos of the South Carolina campaign was clear on Thursday alone.

Texas Gov. Rick Perry dropped out of the race and endorsed Gingrich, who had to fend off his ex-wife's accusations that he had asked her for an "open marriage." Romney, meanwhile, spent the day repeatedly resisting calls to release his tax returns immediately. A cantankerous debate — the second of two this week — capped off the surreal day.

Perhaps illustrating the new reality of the race here, the raucous debate audience booed Romney as he answered a question about his refusal to release the tax returns. The crowd gave two standing ovations to Gingrich as he defended himself against his ex-wife's allegations.

All this in a state where the Republican establishment constantly reminds the rest of the nation that "we pick presidents," given that whoever wins South Carolina has gone on to win the party's nomination since the primary was established in 1980.

"I've never seen anything like it. It is funny, I suppose," marveled Colette Kent, a 78-year-old from Fort Mill, who turned out Friday to meet Santorum. She said values were the reason she was backing him, calling the former Pennsylvania senator "a good and decent man" and "a Christian man."

At first glance, the allegations by Gingrich's ex-wife would appear to be deadly in a state smack in the middle of the Bible Belt. But more than a million people have poured into South Carolina over the past 20 years, increasing the population by nearly 33 percent and watering down some of its evangelical fervor.

Stephanie Irick, 55, was among those still sticking by Gingrich. She thinks Romney is a flip-flopper and the allegations by Gingrich's ex-wife didn't shake her support.

"Do I believe it? I don't have a clue," Irick said while at a Gingrich rally in Walterboro on Friday. "What goes on in people's bedroom is their own business."

Others said the timing smelled bad.

"This comes out now, after he's been running how long? It doesn't seem like a coincidence," said Mike Smith, 52. The Fort Mill resident who backed President Barack Obama over Sen. John McCain four years ago planned to vote for Santorum. Smith shrugged at the rollicking nature of the race, saying the real issues were about paying the mortgage and feeding families.

"Everything else is a distraction," he said. "We need jobs, not gossip."

That's what Gingrich seemed to argue at Thursday's debate in Charleston when he tore into CNN moderator John King for making the opening question about Gingrich's former wife.

A few days earlier at a debate in Myrtle Beach, Gingrich also earned the biggest cheers of the night by tangling with Fox News Channel contributor Juan Williams, who asked Gingrich to defend his comments that Obama was "the greatest food stamp president." Williams also asked Gingrich to defend as not racist his suggestion that poor children could earn money by doing janitorial work at their schools.

"He hit that out of the park. It has nothing to do with race," said 62-year-old Ed Cheek, a hospital chaplain who was at a Santorum rally Friday in Lexington but planned to vote for Gingrich.

Santorum, for his part, has been presenting himself as a good alternative to voters bothered by Gingrich's three marriages and affairs and who think Romney is too moderate.

Deborah Braun was at Santorum's rally because she thinks he can beat Obama and has the kind of values she wants in a president. The 62-year-old mother of five and grandmother of 10 said Gingrich "has too much baggage. He's not trustworthy."

All the discussion of tax returns and cheating spouses have drowned out Paul's supporters.

"He is ready to do the hard things that we need to do to turn things around," said David Oberly, a 40-year-old geologist who was eating lunch in a West Columbia restaurant. "I don't care what a person does in their private life. It's issues that matter."

There was one final wrinkle that has turned the South Carolina race into even more of a circus.

Comedian Stephen Colbert attracted thousands to a rally Friday in his hometown of Charleston. Write-ins aren't accepted on the ballot, so Colbert is asking his supporters to vote for Herman Cain, who dropped out of the race last month.

Caroline Simmel attended Colbert's rally. The 18-year-old College of Charleston student voting in her first election said the events of the past few days had left her more confused.

"I don't know that I like any of the candidates out there right now," Simmel said. "I think I would rather have Stephen Colbert running the country."

Associated Press writers Charles Babington in Lexington, Philip Elliott in Fort Mill, Shannon McCaffrey in Walterboro and Bruce Smith in Charleston contributed to this report.