Hillary Clinton and Bernie Sanders clashed in their first one-on-debate on the White House trail, with the two Democrats adopting a confrontational tone.
Mrs Clinton accused Mr Sanders of subjecting her to an "artful smear" while he suggested the former secretary of state was a captive of America's political establishment.
The two Democrats embraced a markedly more contentious tone than when they last debated before the year's presidential voting began in Iowa.
It showed how the race for the nomination has tightened five days ahead of the first-in-the-nation primary in New Hampshire next Tuesday.
The two argued over ideas, over tactics and over who has the liberal credentials to deliver on an agenda of better access to health care, more affordable college, fighting income inequality and more.
It was Mrs Clinton who was the main aggressor, saying Mr Sanders could never achieve his ambitious and costly proposals.
She went after the Vermont senator for his efforts to cast her as beholden to Wall Street interests because of the campaign donations and speaking fees she has accepted from the financial sector.
"It's time to end the very artful smear that you and your campaign have been carrying out," she said.
Mr Sanders, for his part, suggested Mrs Clinton's loyalties were coloured by a reliance on big corporate donors.
"Secretary Clinton does represent the establishment," he said. "I represent - I hope - ordinary Americans."
Mrs Clinton may say the right things, he suggested, but "one of the things we should do is not only talk the talk but walk the walk".
He added: "I am very proud to be the only candidate up here who does not have super PAC, who's not raising huge sums from Wall Street and special interests," referring to outside groups who can receive unlimited funds to support candidates.
Where Mrs Clinton aimed considerable criticism at Mr Sanders, the Vermont senator focused much of his fire on what he says is a political system rigged against ordinary Americans.
Mrs Clinton, unwilling to cede the issue to Mr Sanders, insisted her regulatory policies would be tougher on Wall Street than his.
She said: "I've got their number, the Wall Street guys."
The debate was the first face-off for Mrs Clinton and Mr Sanders since former Maryland governor Martin O'Malley dropped out of the race after a poor showing in Iowa.
The close result in Iowa was the latest twist in an election campaign that, until recently, had been dominated by the crowded and noisy field of Republicans, who spread out across New Hampshire this week.
Donald Trump, who finished second in Iowa, stepped up the pace of his campaign and acknowledged he should have had a stronger ground operation in Iowa.
Jeb Bush, his campaign lagging, brought in his mother, former first lady Barbara Bush, who praised him as "decent and honest and everything we need in a president".
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