Clinton said that Obama's argument that her plan would penalize Americans who could not afford to join the Clinton plan was "false, misleading and discredited." Obama took strenuous exception to her insistence that his plan would leave out 15 million Americans.
"I think it's very important to understand the context of this, and that is that Sen. Clinton has, in her campaign at least, has constantly sent out negative attacks on us, e-mail, robocalls, fliers, television ads, radio calls, and we haven't whined about it because I understand that's the nature of this campaign," he said.
After the candidates' painstaking review of their plans, moderator Williams dryly observed: "Well, a 16-minute discussion on healthcare is certainly a start."
Threaded throughout the debate was the central question before Democratic voters Tuesday and, if the race is not decided, on through the spring: Will it be Clinton's marriage of traditional experience and pugilistic instincts, or Obama's lighter resume and promise to forge a unified political movement?
Using her past quarrels over universal healthcare as an example, Clinton said that "it takes a fighter" to turn words into action.
"The special interests are not going to give up without a fight," she said. "And I believe that I am a fighter, and I will fight for the people of Ohio and the people of America."
Obama said that Clinton's effort to push a universal healthcare plan beginning in 1993 was doomed in part because she kept even other Democrats at arms' length.
"Sen. Clinton ended up fighting not only just the insurance companies and the drug companies, but also members of her own party," he said.
The war in Iraq, which has been central to many of the Democratic debates, arose again with Clinton arguing, essentially, that Obama's early opposition to the war -- when he was in the Illinois state senate -- did not count.
"He didn't have responsibility; he didn't have to vote," Clinton said, adding, "when he came to the Senate, he and I have voted exactly the same."
Obama said his Senate votes, to secure funding for troops, were akin to the limited ways one has to get a bus out of a ditch -- implying that Clinton was among the drivers.
"The question is, who's making the decision initially to drive the bus into the ditch?" he asked, adding later, "The fact is that Sen. Clinton often says that she is ready on Day One [to be president] but, in fact, she was ready to give in to George Bush on Day One on this critical issue."
Russert pressed each candidate on matters of personal accountability, to little avail.
He noted that Obama agreed last year to accept public financing -- and the attendant spending limits -- as the Democratic nominee. Now, he said, "you seem to be waffling."
Obama -- who has shattered fundraising records in the primary campaign -- declined to renew his pledge, but promised as the nominee to "sit down with John McCain and make sure that we have a system that is fair for both sides."
Russert asked Clinton about why she has not released her income tax returns, especially in light of the $5 million she lent her campaign earlier this month.
"I will release my tax returns," Clinton replied.
"Why not now?" Russert asked.
"I will do it as others have done it, upon becoming the nominee or even earlier," Clinton said, adding, "I'm a little busy right now."
Clinton and Russert worked together in one instance: After Russert asked Obama his views on his endorsement by Nation of Islam leader Louis Farrakhan, in light of his anti-Semitic remarks, the Illinois senator said he had denounced Farrakhan's comments.
Clinton fired back that during her New York race, under similar circumstances, she had "rejected" the support of anti-Semitic individuals.
"If the word 'reject,' Sen. Clinton feels, is stronger than the word 'denounce,' then I'm happy to concede the point, and I would reject and denounce," Obama replied.
"Good. Good. Excellent," Clinton said.
Barabak reported from Cleveland and Decker from Los Angeles.