While Clark is still a largely unknown quantity, Dean offers rivals a thick file of material after serving five terms as governor. Opposing campaigns also have been picking over his statements from several months on the campaign trail.
Their attacks on his stance on taxes, health care and trade were not new, and Dean was prepared for the criticism. His ire was provoked, however, when Missouri Rep. Dick Gephardt accused him of siding with former House Speaker Newt Gingrich — nemesis of the Democrats — in a fight over Medicaid in the mid-1990s.
"You've been saying for many months that you're the head of the Democratic wing of the Democratic Party," Gephardt said. "I think you're just winging it."
Dean grew visibly angry, mouthing, "That's false," while Gephardt spoke.
"I've done more for health insurance, Dick Gephardt, frankly, than you ever have, because I've delivered it to a lot of seniors and a lot of young people," Dean said. "And I'll stake my record on health insurance against anybody up here."
Still short on specifics, Clark seemed to hold his own, reports CBS News Correspondent Byron Pitts. Eight days since he announced his candidacy for president, the four-star general has soared to the top tier in the pack of Democratic contenders in national polls. Clark even beats President Bush in survey.
From the start of the debate Clark acknowledged his political inexperience — "my nine days in politics," as he put it, with a smile.
He avoided the issue of financing the reconstruction of Iraq. He also pleaded ignorance on health care policy — "I don't have a complete package" — and stepped around questions about home mortgages and other issues.
His rivals did not challenge the retired Army general's newness to the party, his changing statements on the war with Iraq or his undeveloped positions on other issues.
"I am pro-choice. I am pro-affirmative action I'm pro-environment and pro-health. I believe the United States should engage in allies and we should be a player in the international community and use force only as a last resource," Clark said. "That's why I'm proud to be a Democrat."
"I think they want to take Dean out so I think the attacks were on dean as opposed to on Clark. If Clark looks more serious in Iowa and New Hampshire, he'll be attacked as we move further down the line," Republican strategist Ed Rollins told CBS News' The Early Show.
"We've got a man who recklessly cut taxes. We've got a man who recklessly took us into war with Iraq," Clark said. "If George Bush rebuilds Iraq the way he rebuilds the U.S., they're going to lose 3 million jobs over the course of the next two years."
"I think (Clark) having to prove he's a Democrat in a Democrat debate is the first step that leaves some doubts," Rollins said.
Dean complained that his own Democratic credentials were under fire.
North Carolina Sen. John Edwards took Dean to task for calling for a repeal of all of Mr. Bush's tax cuts. Edwards, along with Sens. John Kerry of Massachusetts and Joe Lieberman of Connecticut, said Dean's plan would result in higher taxes for the middle class.
Kerry, who is chasing Dean in New Hampshire polls, also criticized him for taking credit for balancing Vermont's budget and for saying that the United States should insist its trading partners have equal labor and environment standards.
Ohio Rep. Dennis Kucinich said he was surprised that Dean, a medical doctor, would promote a health insurance plan that doesn't cover every American. Neither do the plans offered by Kerry, Gephardt, Edwards or other candidates, but Kucinich only singled out Dean.
Dean said his rivals are portraying him inaccurately.
"You know, to listen to Senator Lieberman, Senator Kerry, Representative Gephardt, I'm anti-Israel, I'm anti-trade, I'm anti-Medicare and I'm anti-Social Security," he said. "I wonder how I ended up in the Democratic Party."
New York activist Al Sharpton pleaded with Dean not to get too personal, and Edwards also asked that the Democrats focus their fire on Mr. Bush.
"We need to be really careful that our anger is not directed at each other," Edwards said.