PHILADELPHIA -- Trailing in national polls and with supporters growing restless, Barack Obama challenged Hillary Rodham Clinton's electability and candor in a spirited debate last night. But the Illinois senator failed to rattle the front-runner or do much, it seemed, to shake up the Democratic presidential race.
Under fire from the first question, the New York senator smiled through most of the two-hour session, often seconding the views of others on stage and joining the laughter during an attack on Republican Rudolph W. Giuliani.
The sharpest exchange centered on suggestions that Clinton was too divisive to win the White House. She said Republicans' focus on her candidacy showed - "in a perverse way" - its strength. "They obviously think that I am communicating effectively about what I will do as president," Clinton said.
"Part of the reason that Republicans, I think, are obsessed with you, Hillary, is because that's a fight they're very comfortable having," Obama responded moments later. "It's the fight that we've been through since the '90s. ... And what we don't need is another eight years of bickering."
John Edwards, the aggressor throughout most of the evening, was even harsher. "Will she be the person who brings about change in this country?" asked the former North Carolina senator. "You know, I believe in Santa Claus. I believe in the tooth fairy, but I don't think that's going to happen. I really don't."
But for the most part, the candidates spent the night rehashing old arguments over Iraq, Iran and Social Security.
Some candidates expressed frustration that most of the questions were directed to Clinton, Obama and Edwards. Seventeen minutes into the debate, Ohio Rep. Dennis J. Kucinich had yet to get a question and blurted out, "Is this a debate here?" Minutes later, New Mexico Gov. Bill Richardson threw up his hands in protest that he hadn't been called on either and exchanged a frustrated glance with Kucinich.
At one point, Richardson chided others for ganging up on Clinton. "We need to be positive in this campaign," he said, as Clinton stood behind a nearby lectern, nodding in agreement. "Yes, we need to point out our differences ... but I think it's important we save our ammunition for the Republicans."
The session at Drexel University - the seventh time the Democratic hopefuls, which include Sens. Joseph R. Biden Jr. of Delaware and Christopher J. Dodd of Connecticut, have shared a debate stage - came at a vital time in the race, which appears split into parallel contests: one taking place in Iowa and the other nationally.
Clinton, Obama and Edwards are tightly bunched in Iowa, which will begin the presidential balloting Jan. 3. Meanwhile, Clinton has opened a yawning gap in national polls as well as in New Hampshire, the first primary state. That has intensified pressure on Obama to translate his big budget and campaign-trail charisma into greater support. The best way to do that, he acknowledged, was to draw sharper distinctions with Clinton.
But while he took issue with Clinton several times - suggesting she fuzzed up her position on Social Security and criticizing the slow release of documents from her husband's administration - he did so in a tone suggesting he was back in the classroom teaching a course on constitutional law.
The only person on stage who appeared to leave Clinton unnerved was co-moderator Tim Russert of NBC, who pressed the senator on the Social Security issue. Clinton has said in public forums that she would not raise the cap on Social Security taxes, now set at earnings up to $97,500. But Russert cited an instance in which a reporter overheard her telling an Iowa voter that she would consider raising the cap for high-income earners.
"Why do you have one public position and one private position?" Russert asked.
"Well, Tim, I don't," Clinton replied, saying the steps she favored were restoring "fiscal responsibility" to Washington and then appointing a bipartisan panel to examine ways to shore up the program. "I don't want to balance Social Security on the backs of our seniors and middle-class families. That's why I put fiscal responsibility first."
As for Edwards, he faces a win-or-go-home situation in Iowa, where he charmed audiences four years ago by shunning negative campaigning in his first bid for president. This time, Edwards has been far more pugnacious, taking the lead among Democrats in assailing his rivals.
In one of the night's most pointed attacks, he suggested that Clinton was weighing her stance on issues such as Iran with an eye on moving from "primary mode to general election mode. I think that our responsibility as presidential candidates is to be in tell-the-truth mode all the time."
But even Edwards holstered the harsher rhetoric he often uses on the campaign trail.
Mark Z. Barabak and Peter Nicholas write for the Los Angeles Times. The Associated Press contributed to this article.