US Democrat Hillary Clinton has gone on the attack against rival Bernie Sanders in their most contentious presidential debate yet.
Clinton questioned whether his ambitious proposals were viable and said it was unfair to question her liberal credentials.
Sanders fought back repeatedly, accusing Clinton of representing the political establishment during a debate that featured sharp differences over health care, university tuition funding and efforts to rein in Wall Street.
The intensity of the exchanges reflected a race that has seen Clinton's once prohibitive lead shrivel against a relatively unknown underdog in the battle over who would best lead the Democratic Party in the November 8 election and who could deliver on the party's liberal agenda.
Clinton said Sanders' proposal for single-payer universal healthcare coverage would jeopardise Obamacare, calling it "a great mistake", and she said his plans for free college education would be too costly to be realistic.
"I can get things done. I'm not making promises I can't keep," Clinton said.
Sanders said he would not dismantle Obamacare but would expand it, pointing to how many other countries provide universal healthcare.
"I do not accept the belief that the United States of America can't do that," Sanders said. "By moving forward, rallying the American people, I do believe we should have health care for all."
Sanders said his proposal for free tuition at public universities would be paid with a tax on Wall Street speculation.
"The middle class bailed out Wall Street in their time of need. Now, it is Wall Street's time to help the middle class," he said.
Five days before New Hampshire holds the second of the state-by-state presidential nominating contests, polls show Sanders, a US senator from neighbouring Vermont, has a double-digit lead over Clinton after surprising the front-runner by finishing just barely behind her in Iowa on Monday (local time).
Sanders accused Clinton of representing "the establishment", while saying he represented "ordinary working Americans".
He also noted her Super PAC had taken contributions from Wall Street firms and that Clinton has received speaking fees from Goldman Sachs.
Clinton called that an "artful smear" and said she had never changed a view or a vote because of donations.
"Enough is enough. If you've got something to say, say it directly," Clinton told Sanders.
She also disputed the establishment label, saying it was "quite amusing" to accuse "a woman, running to be the first woman president, as the establishment".