"I did not vote for George Bush. I voted for Al Gore," Clark retorted in the most contentious of four debates thus far in the battle for the nomination for the White House.
Sen. John Kerry, Sen. Joe Lieberman and former Vermont Gov. Howard Dean criticized Clark, who jumped to the head of the pack in several national polls within days of entering the race less than a month ago.
Dean said Clark had advised a Democratic congressional candidate in New Hampshire last year to vote for legislation supporting the war in Iraq — a war the former general now criticizes sharply.
Lieberman, a supporter of the war, jabbed at Dean and Clark simultaneously. In a backhanded compliment, he said Dean had been steadfast in his opposition to the war.
By contrast, he criticized Clark for what he called a history of inconsistency on Iraq. He said Democrats need a candidate who can "reach a conclusion and stick to it."
Kerry said that despite Clark's declarations, the former Army general "did say he would vote for the resolution" approving the war. He also said Clark had praised Bush at a Republican fund-raiser last year — at a time, he said, the administration had already won tax cuts for the rich from Congress and was trying to tap into the Arctic National Wildlife Refuge in Alaska for oil.
Sen. John Edwards of North Carolina also spoke dismissively of Clark, mentioning that he had always opposed Bush — even "when some on this stage had hope for" him.
Clark labored to fend off the criticism. "I would never have voted for war. The war was an unnecessary war and it's been a huge strategic mistake for the country," he said.
At one point, Clark struck an above-the-fray pose, saying, "I'm not going to attack a fellow Democrat," he said.
But even that drew a sharp response.
"I want to say ... welcome to the Democratic presidential campaign. Look, none of us are above questioning," said Lieberman.
The field of Democratic contenders — shrunken by one with Florida Sen. Bob Graham's withdrawal from the race — met onstage at the Orpheum Theater in Phoenix, capital of a state that holds an early primary on Feb. 3.
The candidates sat on tall chairs in front of identical lecterns, each one bearing a CNN logo. The cable network sponsored the debate, and Judy Woodruff, a network anchor, served as moderator.
When they weren't sparring with one another, Democrats took time to heap fresh criticism on Bush's postwar policy in Iraq, faulting him for failing to win significant help from other countries.
"You remember on your report card you had your English grade, your history grade and then it said, plays well together? He flunked that part," jabbed Rep. Dick Gephardt of Missouri.
Dean accused several rivals of giving Bush "a blank check to go to war in Iraq" by voting for or voicing support for a congressional resolution last year.
But Dean also said he would support Bush's request for $87 billion to maintain the troops stationed in Iraq and help rebuild the country.
That, in turn, drew a challenge from Ohio Rep. Dennis Kucinich, who said the troops should be brought home because "they are targets" for terrorists in the land that Saddam Hussein once ruled.
Edwards sought to make the case that his working class background as a millworker's son made him the best candidate to defeat Bush.
Kerry of Massachusetts, who grew up wealthy and remains that way, quickly rebutted that. "In Vietnam, nobody cared about your background," said the war veteran.
Halfway through the debate, the format switched.
The lecterns disappeared, the men shed their suit jackets and fielded questions from the audience. The first one came from a veteran of Iraq who asked what the Democrats would do for military families.
All nine raised their hands and Clark, a former NATO commander, drew laughter when he eagerly sought the floor.
"God bless you," Lieberman said to the questioner when it came time for him to speak.
It marked the first time in any of the debates that the candidates were asked to respond to questions from men and women whose votes will prove decisive in the early primary states.