Hillary Clinton has locked horns with her rival for the Democratic White House nomination Bernie Sanders in a party debate, saying his promises "don't add up" and accusing him of smear tactics.

Their duel in New Hampshire on Thursday night came three days after Clinton clinched the narrowest victory in Iowa caucus history against Sanders, and five days before the next round of voting in the tortuous US presidential race.

"Senator Sanders and I share some very big progressive goals," the former secretary of state said as the debate got under way. "But the numbers just don't add up from what Senator Sanders has been proposing.

"I am not going to make promises I can't keep."

While most expect Clinton to ultimately win the nomination, Sanders has whipped up passionate support with a grassroots campaign focused on improving the lives of working Americans.

With the senator from Vermont leading by 20 points in the New Hampshire polls, the pair tussled over their claim to represent the progressive wing of the party, and their differences on Wall Street, healthcare and taxes.

Andrew Smith, the director of the University of New Hampshire Survey Center, told Al Jazeera that while Clinton performed strongly on Thursday night, she was not expected to win the primary.

"I think she did a really good job. Whether she was able to ... make this a close race? I don't think so," Smith said. "If she can get this into single digits, it could be considered a win for her."

Some of their sharpest exchanges were on campaign financing, with Clinton accusing her rival of seeking unfairly to discredit her by suggesting she was beholden to powerful donors.

Sanders insisted that Clinton cannot claim to be both a moderate and a progressive, criticising her for raising $15m from Wall Street.

"I think it's time to end the artful smear that you and your campaign have been carrying out in recent weeks and let's talk about the issues that divide us," she responded. "I never changed a vote because of any donation I received."

READ MORE: Al Jazeera's comprehensive coverage of the 2016 US presidential campaign

"I really don't think these kinds of attacks by insinuation are worthy of you. Enough is enough!"

But Sanders stood firm, repeating his oft-voiced pledge to rein in billionaires' influence on the US political system.

"Let's talk about issues," he said. "Let's talk about why in the 1990s Wall Street got deregulated. Did it have anything to do with the fact that Wall Street provided - spent billions of dollars on - lobbying and campaign contributions?

"Well, some people might think that had some influence."