Presidential hopefuls Hillary Clinton and Barack Obama agreed on major issues but clashed over each other's track records in a crackling debate one week before a pivotal set of Democrat primaries.

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Democratic presidential hopeful Hillary Clinton listens as rival Barack Obama responds to a question during a Democratic presidential debate Tuesday in Cleveland, Ohio. ((Mark Duncan/Associated Press))

The tone of the debate in Cleveland, Ohio, was polite yet pointed, increasingly so as the 90-minute session wore on, a reflection of the stakes in the race to be Democratic nominee in the U.S. presidential race.

Obama, an Illinois senator, has won 11 straight primaries and caucuses and New York Senator Clinton, a former first lady, is in desperate need of a comeback. Crucial primaries in Texas and Ohio are on March 4.

The two rivals on Tuesday heatedly debated NAFTA, the free trade agreement with Canada and Mexico that is wildly unpopular with blue-collar workers, whose votes are critical in the Ohio Democratic primary.

Neither candidate said they were ready to withdraw from the agreement, although both said they would use the threat of withdrawal to pressure Mexico to make changes.

"I have said I would renegotiate NAFTA," said Clinton. "I will say to Mexico that we will opt out of NAFTA unless we renegotiate it."

Obama said Clinton has tried to have it both ways, touting the trade deal in farm states where it's popular while finding fault with it in places like Ohio. Obama has also called for NAFTA to be renegotiated.

"This is something I have been consistent about," said Obama, who said he went to the American Farm Bureau Federation to tout his opposition to NAFTA, and used it as an issue in his 2004 Senate campaign.

"That conversation I had with the farm bureau, I was not ambivalent at all," said Obama.

Clinton denies ties to turban photo

The two rivals, the only survivors of a gruelling primary season, sat about a foot apart at a table on stage at Cleveland State University. It was the 20th debate of the campaign, 10 months to the day after the first.

The race was far different in April 2007, when Clinton was the front-runner by far. Now Obama holds that place, both in terms of contests and delegates won.

Clinton insisted during the debate that as far as she knew, her campaign had nothing to do with circulating a photograph of Obama wearing a white turban and a wraparound white robe presented to him by elders in Wajir, in northeastern Kenya.

The gossip and news website the Drudge Report posted the photograph Monday and said, without substantiation, that it was being circulated by "Clinton staffers."

"I take Senator Clinton at her word that she knew nothing about the photo," Obama said.

Candidates slam Bush record in Iraq

On the Iraq War, both candidates denounced U.S. President George W. Bush's record, then restated long-held disagreements over which of them is more opposed.

Clinton said she and Obama have had virtually identical voting records on the war since he entered the U.S. Senate in 2005.

Clinton voted in 2002 to authorize the war, at a time when Obama was not yet in U.S. Congress, and he tried to use the issue to rebut charges that he is ill-prepared to become commander in chief.

"The fact is that Senator Clinton often says that she is ready on Day 1, but, in fact, she was ready to give in to George Bush on Day 1 on this critical issue," Obama said.