The bill they were referring to, passed by both the House of Representatives and Congress, says that US troops should begin to leave the Middle Eastern country in October this year, with withdrawal to be completed by March 2008.
But Mr Bush has already said he will veto the bill after it failed to gain the required two-thirds majority to trump his constitutional right.
In last night's 90-minute debate in South Carolina – which will be the first state to hold its primary election next year – strict 60-second limits on answers and a ban on follow-up questions restricted the candidates to any serious attacks and allowed them to sidestep potentially hazardous issues.
Barack Obama still questioned New York senator Hillary Clinton over her decision to initially back the Iraq war.
"If this president does not get us out of Iraq, when I am president, I will," Mrs Clinton, who leads opinion polls ahead of Mr Obama, responded.
"We have given the Iraqi people the chance to have freedom, to have their own country. It is up to them to decide whether or not they're going to take that chance."
Illinois senator Mr Oboma said he was "proud" to have opposed the war from the start, but referring to Mr Bush's expected veto he insisted that the US was now "one signature away from ending this war".
"The American people have said, Republicans and Democrats, that it's time to end this war."
Along with Mrs Clinton and Mr Obama, Joe Biden, Chris Dodd, John Edwards, Mike Gravel, Dennis Kucinich and Bill Richardson are bidding to become the Democrats' nominee for next year's elections, with one of Mitt Romney, John McCain, Rudy Giuliani the likely Republican candidates.
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