A potentially record-breaking number of voters headed to the polls in South Carolina Saturday to sort out the tense and racially charged Democratic contest, as the three candidates each jockeyed for a critical boost before the tidal wave of primaries and caucuses Feb. 5.

Polls close at 7 p.m. ET, and state Election Commission spokesman Chris Whitmire told FOX News officials were even seeing more Democrats stream out Saturday than during the GOP primary last week. It's usually the reverse, since South Carolina is a Republican stronghold.

Whitmire said they were seeing "steady to heavy turnout," and that a record-breaking turnout of 350,000 is possible.

Polls opened at 7 a.m. and election officials reported no problems with voting machines as there were in last week's GOP primary after one county's electronic machines failed to function properly.

South Carolina offers 45 Democratic National Convention delegates allotted proportionately. It is also the first state to offer an indication of Barack Obama's political appeal among large African-American communities.

But as Obama and Hillary Clinton have sparred intensely in the state, underdog John Edwards is also looking for an edge, claiming he's the well-mannered alternative to his squabbling rivals.

Obama doesn't just want to win the South Carolina primary, though. He wants to do it in such a way that proves he's got broad appeal across lines of race, gender and economic status and sets himself up as a stiff rival to Hillary Clinton in the diverse and numerous delegate-rich states voting on Feb. 5.

Surveys showed Obama leading by more than 10 points in the state ahead of the vote, but the issue of race has been a persistent subtext in the first primary to feature a large number of black voters. Though Hillary Clinton returned to South Carolina after campaigning in other major states holding upcoming contests, Bill Clinton has suggested his wife may be at a disadvantage because of voters picking candidates along racial lines, and that this could push Obama to victory.

Polls, in fact, show Obama has strong support among South Carolina's black voters, who are expected to compose more than 50 percent of the electorate, and diminishing support among white voters. But the Illinois senator is trying to fight any perception that his appeal is narrowly tailored.

"After we won Iowa, everybody was so excited," Obama said at a rally in Columbia, S.C., Friday night. "Everybody said, 'Oh, look at this. You know, African American, he's winning in a state with almost no African Americans,' and everybody's excited, and young people came out. And I think people started thinking, 'Well, you know this isn't hard,' - but you know what, the status quo does not give up that easily."

He told supporters the campaign was "poised to make a little bit more history" Saturday.

Click here to see photos from South Carolina's Democratic primary.

South Carolina is widely considered a must-win for Obama, after his breakout Iowa caucus victory Jan. 3 was overshadowed by Clinton's so-called consecutive comebacks in New Hampshire and Nevada. A new victory could help reinforce Obama's co-frontrunner status with Clinton, while a loss would severely imperil his candidacy.

And a victory by a wide margin, carried on the backs of a broad cross-section of voters, would serve an even bigger purpose.

FOX News entrance polls from the Nevada caucuses last Saturday demonstrated the demographic divide, showing Clinton held strong leads among female voters, white voters and senior voters, while Obama was the pick for 83 percent of black voters.

Obama spent Saturday morning greeting South Carolina residents at a predominately black Baptist church and at historically-black Benedict College in Columbia, S.C. Later, he surprised lunchgoers at Harper's restaurant who posed for pictures with him and shook his hand.

For her part, Clinton was already looking ahead to Feb. 5 even as the South Carolina primary loomed. She campaigned in California, Arizona and New Jersey early in the week before returning to South Carolina on Thursday. She was headed to Tennessee after the polls close here Saturday.

Clinton and daughter Chelsea greeted voters Saturday morning at a Shoney's restaurant in Columbia. Clinton hoisted babies and wedged into booths to chat with patrons surprised to have their breakfast interrupted by a presidential candidate and a huge media horde.

Obama's campaign has been cautiously optimistic about Saturday, since Clinton defied early polls to win New Hampshire Jan. 8 -- but Clinton's campaign released a memo Saturday scolding Obama for his confidence in South Carolina while still managing expectations for her own turnout.

"The Obama campaign has been so confident of winning South Carolina that six months ago they flatly predicted victory in the Palmetto State," the memo said. "Despite Senator Obama's large lead, Senator Clinton has campaigned across the Palmetto State, reaching out and asking for each and every vote. She has heard directly from South Carolinians about their concerns and their hopes for a stronger, more prosperous America.

"Regardless of today's outcome, the race quickly shifts to Florida, where hundreds of thousands of Democrats will turn out to vote on Tuesday."

Clinton has been trying to get Florida's convention delegates reinstated, even though they were stripped by the national party. The campaign claims this will be a delegate fight, even after South Carolina.

Interest in the race, though, was threatened by recent intra-party bickering.

Bill Clinton stepped into a starring role in South Carolina -- aggressively challenging Obama's record while scolding the media for what the former president said was unfair coverage of the contest.

Bill Clinton complained that reporters cared too much about the racial aspect of the campaign even as he predicted Obama would win here because of his race. His high-profile role left Obama to complain that he didn't know which Clinton he was running against.

Bonnie Hix said she voted for Clinton because she believes the former first lady can better cope with adversity. She said she wanted to vote for experience over personality and looked forward to Bill Clinton returning to Washington.

"Any help he can give would be wonderful," said Hix, a 59-year-old museum curator from Columbia who is white.

Edwards, who has pinned his fading hopes on his native South Carolina, campaigned actively in the state throughout the week and was hoping for a nudge out of the Obama-Clinton bickering.

"I think that voters are ... sick and tired of politicians who spend all their energy fighting with each other," Edwards told FOX News Saturday.

Edwards smiled into TV cameras Saturday morning at a Charleston diner but acknowledged he had dim prospects to score a win as polls showed him third in the state he carried in 2004 against well-financed, high-profile rivals.

Nonetheless, the former North Carolina senator said he had some reason for optimism.

"I think things have shifted some this week," Edwards said during one television interview, and later said in another that he's "very much the underdog."

One poll out this week showed Edwards picking up some support among whites as Obama's support from whites slipped after a week of steady criticism from Clinton and her husband.

Edwards said he is "opposed to anything that divides this state based on race."

He told reporters at a Mount Pleasant restaurant that he's still in the race, no matter how he fares Saturday.

"The role I want to play is president of the United States," he said.

The run-up to the primary was noteworthy for its nasty tone -- from a rancorous televised debate early in the week to the first negative ads of the campaign.

Clinton and Obama clashed bitterly in a televised forum Monday in Myrtle Beach, chiding one another on issues of character and trustworthiness. Edwards tried to rise above the rancor while pleading for equal air time.

The two leading candidates also squared off in a pair of radio ads -- Clinton's challenging Obama's claim that Republicans were once "the party of ideas," and Obama's saying the former first lady would "do anything" to be elected. The ads stayed up only briefly.

FOX News' Caroline Shively, Major Garrett and Bonney Kapp and The Associated Press contributed to this report.