The war in Iraq has divided Democratic party presidential candidates during their second head-to-head live TV debate ahead of the 2008 US election.
Exchanges between the eight hopefuls at the debate in New Hampshire featured repeated calls for a US withdrawal.
There were also clashes over whether President George W Bush had made the US safer from terrorism since 9/11.
New Hampshire will play host to the Republican party's candidates for their third televised debate on Tuesday.
The state will be the first to vote in national primary elections early next year, from which the Democratic and Republican candidates chosen to fight it out for the White House in November 2008 will be chosen.
'I was wrong'
Sunday's debate at St Anselm College in Manchester was moderated by CNN news anchor Wolf Blitzer, joined by Tom Fahey from local daily The Union Leader and Scott Spralding from TV station WMUR.
In the first hour of the two-hour debate, the candidates were each asked questions by Mr Fahey and Mr Spralding.
In the second half an audience of undecided New Hampshire voters took over.
The front-runners in the battle to win the Democratic nomination - New York Senator Hillary Clinton, Illinois Senator Barack Obama and former senator John Edwards - were among the first to clash.
Mr Edwards, who is trailing Senator Clinton and Senator Obama in the national polls, went on the offensive during the debate, attacking them both for a timid approach to enforcing President Bush to bring home troops from Iraq.
He said neither of them in their role as senators had spoken out loudly and clearly against legislation which failed to commit to a withdrawal date.
"There is a difference between leadership and legislating," he said.
Senator Obama responded to Mr Edwards's remarks by pointing out that he and Senator Clinton had voted in October 2002 in favour of the US-led invasion.
"I opposed this war from the start. So you're about four-and-a-half years late on leadership on this issue," said Senator Obama, who was not in the Senate in 2002.
"He was right, I was wrong," Mr Edwards conceded.
Senator Clinton continued to refuse to say her support for the invasion had been wrong at the time.
"That was a sincere vote," she said.
Nevertheless, she vowed to withdraw US forces and blamed President Bush for the current situation.
"This is George Bush's war. He is responsible for this war, he started the war, he mismanaged the war, he escalated the war and he refuses to end the war," she said.
The candidates also vowed to refocus the Bush administration's so-called war on terror, a day after US officials said they had exposed a plot to blow New York's John F Kennedy Airport.
After Mr Edwards called the war on terror a "political slogan, a bumper sticker", Senator Clinton said she disagreed.
"As a senator from New York, I have seen first hand the terrible damage that can be inflicted on our country by a small band of terrorists," she said.
"I believe we are safer than we were."
But Senator Obama said the war in Iraq had detracted from efforts to combat global terrorism.
"All of us are glad that we haven't had a terrorist attack since 9/11, and I think there's some things that the Bush administration has done well," he said.
"But, we live in a more dangerous world partly as a consequence of this president's actions."
Other topics discussed in the debate included the economy, immigration, national security, climate change and healthcare reform.
The BBC's James Coomarasamy says Sunday's contest was more free-flowing and substantive than when they first lined up in South Carolina in April.
But in general the Democrats remained keen to present a united front, perhaps none more so than Hillary Clinton who remains ahead in the national polls and seems likely to remain so after another assured performance, our correspondent says.
On Tuesday, the 10 Republicans seeking their party's nomination will debate the same top issues of the day.