But days before a 10-state showdown that could all but end the race for the Democratic nomination, Edwards largely avoided confrontation, Kerry was complimentary to his fellow senator and the two focused their ire on Mr. Bush.
Edwards had hoped Thursday night's debate would help emphasize differences in an attempt to galvanize support and narrow the large gap with the front-running Kerry.
"I know he's looking for some differences because you need them," Kerry chided Edwards at one point.
There were differences on the death penalty, which Edwards supports and Kerry opposes, and on trade, which Edwards has said is costing American jobs.
CBS News Anchor Dan Rather will moderate a debate among the four Democratic presidential contenders on Sunday, Feb. 29, at 11:00 AM ET. Watch a live Webcast on CBSNews.com.
The polite tone suggested what the calendar and delegate count indicate: that the Democratic race is winding down.
"There are more groans in a professional wrestling match than there were tonight, we have a rallying Democratic Party," Bob Mulholland, the California Democratic Party's chief strategist, told CBSNews.com Chief Political Writer David Paul Kuhn. "I thought Kerry and Edwards acted like teammates getting ready for the big fall game."
Both senators took nearly identical positions on the gay-marriage issue — voicing personal opposition but saying it should be left for states to decide rather than be banned by a constitutional amendment, as Mr. Bush called for this week.
On the day that celebrity Rosie O'Donnell was married in San Francisco to her longtime girlfriend, Kerry and Edwards both sharply criticized Mr. Bush's call for a constitutional amendment.
"He's doing this because he's in (political) trouble. … He's playing politics with the Constitution of the United States," said Kerry. "This is clearly nothing but politics," said Edwards.
Long-shot Al Sharpton, who along with Dennis Kucinich shared the debate stage, accused Mr. Bush of "gay baiting. … The issue is not who you go to bed with. The issue is whether either of you have a job when you get up in the morning."
Both Kerry and Edwards were campaigning Friday in some of the 10 states with Democratic contests on what is known as Super Tuesday. Kerry was giving a speech in Los Angeles on terrorism and national security before a trip to Oakland, Calif. Edwards was headed to St. Paul, Minn., to meet voters.
Together, next week's primaries and caucuses, stretching from New England to California, offer 1,151 delegates — more than half of the 2,162 delegates needed to clinch the nomination.
Kerry went into the debate with 686 delegates in The Associated Press count, compared to 206 for Edwards, and set his sights on securing the nomination Tuesday. Edwards hopes for a comeback to keep his campaign alive.
"Are you ready to go out and do what we have to do next Tuesday?" Kerry told supporters at a party after the debate. "Don't believe the polls. Don't ever let anyone put a label on me."
Kerry was joined by former California Gov. Gray Davis, who announced that he was endorsing his fellow Vietnam veteran. "I am ready to enlist in the Kerry Army," Davis said.
In the debate, Kerry and Edwards sparred over who has the best chance of defeating Bush in the fall.
Asked if Kerry could connect with Americans, Edwards said: "I think it depends on what is happening in the country at the moment. I know I can."
Edwards, as he does repeatedly on the stump, emphasized his humble origins as the son of a textile mill worker tossed out of work when the factory closed, compared to Kerry's relatively affluent upbringing.
"He's a good man … he'd make a good president. But we come from different places," Edwards said.
In response, Kerry said: "I think John has run a terrific campaign. I appreciate completely where John has come from. I've had experiences that John hasn't had. We all bring to the table our life."
To a question about whether the death penalty was justified for a child killer, Kerry said his instinct "is to want to strangle that person with my own hands." But the former prosecutor said he favors the death penalty only for terrorism cases.
Edwards said some crimes "deserve the ultimate punishment" and cited as an example the killers of James Byrd, a black man who was dragged to death from a pickup truck in 1998 in Texas.
At one point, debate moderator Larry King of CNN asked Kucinich, "Why are you here?"
"I'm offering some substantive change in this country," said Kucinich. He said he did not intend to leave the race, and argued passionately for his plan to pull U.S. troops out of Iraq immediately and implement single-payer health care.
Sharpton said repeatedly that it was important for progressives to vote for him so he will have the delegates to be able to wield influence at the summer convention.
Edwards conceded Kerry's dominance of the race so far; Kerry has won 18 of the 20 Democratic contests. But Edwards said that in primaries where Republicans and independents can vote, they were voting for him.
Kerry disputed that and noted his wins in Tennessee and Virginia, two Southern states Edwards had hoped to win.
Edwards sought to portray himself as tougher on trade and protecting jobs and suggested that, unlike Kerry, he doesn't take campaign contributions from Washington lobbyists.
Kerry retorted that Edwards "raised almost 50 percent of his money" from one group, fellow trial lawyers. He also disputed any major differences with Edwards on trade.
The debate, held at the University of Southern California and sponsored by the Los Angeles Times and CNN, was the eighth of the year. Unlike the others, the contestants sat elbow-to-elbow along one side of a table, with Kerry and Edwards next to each other.
The candidates next face off Sunday, in a debate sponsored by CBS News, WCBS Television, and The New York Times.
"I think the three biggest subjects that candidates want to talk about will be jobs, jobs, and jobs. In that order," said CBS News Anchorman Dan Rather, who will moderate Sunday's debate. Social Security, Iraq and gay marriage are other likely topics.