MYRTLE BEACH, South Carolina (CNN) -- Sharp confrontations over health care and other issues highlighted a debate among the Democratic presidential front-runners Monday night, with the sniping threatening to overshadow substance days before the South Carolina primary.
Sen. Hillary Clinton and Sen. Barack Obama started arguing almost as soon as the debate began.
Sens. Hillary Clinton and Barack Obama engaged in particularly sharp exchanges.
With Obama, the senator from Illinois, polling well in the state -- especially among black voters -- Clinton, the New York senator and former first lady, and former Sen. John Edwards of North Carolina used the debate to put Obama on the defensive over a health care plan they say doesn't offer coverage for everyone.
"If you don't start out trying to get universal health care, we know -- and our members of Congress know -- you'll never get there," said Clinton, who pushed a failed effort at expanding health care when her husband was president.
"If a Democrat doesn't stand for universal health care that includes every single American, you can see the consequences of what that will mean." Watch the back-and-forth over health care »
"I believe the problem is not that folks are trying to avoid getting health care," Obama said. "The problem is they can't afford it."
Obama countered that Edwards has said the plan may have to be paid for, in part, by deducting money from people's paychecks, and he said Clinton has been vague on how her plan would be funded. See what the candidates said on the issues »
Just minutes into the debate, sponsored by CNN and the Congressional Black Caucus Institute, Clinton and Obama -- who rank one and two in national polls -- started with the attacks. See what CNN's political team thought about the attacks »
The exchanges saw the two interrupting each other and turning to direct their responses to each other instead of the panel of moderators.
"It is very difficult having a standup debate with you because you never take responsibility for any vote," Clinton said. She attacked Obama for not supporting a Senate amendment that would have capped the interest rate on credit cards at 30 percent. "It's just very difficult to get a straight answer."
The comment drew boos from Obama supporters.
Obama attacked Clinton for working as "a corporate lawyer sitting on the board of Wal-Mart" while he was a community organizer. Clinton jabbed Obama for representing a "slumlord" when he was a lawyer in Chicago. The exchanges let Edwards, a South Carolina native, cast himself as the candidate more interested in policy discussions than political sniping.
"This kind of squabbling -- how many children is this going to get health care? How many people are going to get education because of this? How many kids are going to get to go to college because of this?" Edwards said to cheers from the crowd. "I respect both of my fellow candidates, but we have got to understand this is not about us personally."
A recent national poll showed 59 percent of black Democrats supporting Obama, who is black, compared to 31 percent for Clinton. That's a sharp increase over earlier in the campaign and a particularly big factor in South Carolina -- where as many as half the voters in the Democratic primary will be black.
Perhaps as a result, Clinton and, at times, Edwards kept Obama on the defensive for much of the two-hour debate's first half. Edwards had joined Obama in going after Clinton in earlier debates.
The candidates outlined plans to jumpstart the economy just as some economists say the nation may be sliding toward a recession. Watch the candidates explain how they'd stimulate the economy »
Clinton said her plan calls for a 90-day moratorium on home foreclosures, a five-year interest rate freeze and tax rebates that would average $650 to millions of Americans.
Obama also called for a tax rebate and additional help for senior citizens that would be delivered with their Social Security checks, and Edwards touted a plan that would begin creating environmentally friendly jobs within 30 days.
Obama provided one of the debate's most light-hearted moments when asked about Nobel Prize-winning author Toni Morrison's comment that Bill Clinton -- Sen. Clinton's husband who, as president, was hugely popular with black voters -- was America's "first black president."
"I would have to investigate more of Bill's dancing ability and some of this other stuff before I accurately judged whether he was, in fact, a brother," Obama said to laughter from the audience and other candidates.
The debate unfolded as the nation observed the anniversary of Martin Luther King Jr.'s birth.
Hours after attending services marking the King holiday, all three candidates noted a desire to carry on the civil rights leader's legacy.
"You have got a son of the South; you've got an African-American. You have a woman -- what better way to celebrate the legacy of Dr. King than to look at this stage right here tonight?" Clinton said.
The first Democratic primary in the South, South Carolina is deemed crucial by the Democratic front-runners; voters go to the polls Saturday.
Clinton, who scored victories in the New Hampshire primary and Nevada caucuses, could use a win to paint herself as the clear front-runner going into the February 5 Super Tuesday primaries.
Obama, who scored a win in the Iowa caucuses, would shift momentum to himself after Clinton's back-to-back wins while Edwards, a native of South Carolina, needs a win to shed the mantle of a perennial third-place finisher behind the other two. E-mail to a friend
CNN's Wolf Blitzer and Bill Schneider contributed to this report.