Democratic presidential rivals Barack Obama and John Edwards attacked front-runner Hillary Clinton in a televised party debate, questioning her honesty, consistency and judgment.
Mr Obama, the Illinois senator, began immediately, saying Ms Clinton had changed her positions on the North American Free Trade Agreement, torture policies and the Iraq war.
Leadership, he said, did not mean "changing positions whenever it's politically convenient".
Mr Edwards, a former North Carolina senator, was even sharper at times, saying Ms Clinton "defends a broken system that's corrupt in Washington DC". He stood by his earlier claim that she has engaged in "doubletalk".
Ms Clinton, standing between the two men, largely shrugged off the remarks, saying she had been the focus of Republican candidates' "conversations and consternation" because she was leading in the polls.
The New York senator and wife of former US president Bill Clinton said she had specific plans on social security, diplomacy and health care.
"I have been standing against the Republicans, George Bush and Dick Cheney," she said, "and I will continue to do so, and I think Democrats know that."
Ms Clinton defended her Senate vote in favour of designating Iran's Revolutionary Guard a terrorist group. Mr Obama, Mr Edwards and others have said Mr Bush could interpret the measure as congressional approval for a military attack.
Mr Edwards caustically challenged Ms Clinton's claim that she stood up to the Mr Bush administration. "So the way to do that is to vote yes on a resolution that looks like it was written literally by the neo-cons?" he said, referring to the neo-conservatives who have supported military intervention in Iraq and Iran.
"In my view, rushing to war — we should not be doing that — but we shouldn't be doing nothing," Ms Clinton said. "And that means we should not let them acquire nuclear weapons, and the best way to prevent that is a full court press on the diplomatic front."
Ms Clinton also was the main focus during a discussion of the Iraq war. Mr Edwards again levelled the toughest charges against the New York senator.
"If you believe that combat missions should be continued in Iraq" without a timetable for withdrawal, Mr Edwards said, "then Senator Clinton is your candidate."
Mr Edwards vowed to have all combat troops out of Iraq "in my first year in office".
Ms Clinton replied forcefully, saying "I stand for ending the war in Iraq, bringing our troops home." She added, however, that "it is going to take time," and some troops must remain to fight al-Qaeda in Iraq.
"I don't know how you pursue al-Qaeda without engaging them in combat," she said.