The former secretary of state accused Sanders of delivering an "artful smear" by suggesting her political favor could be bought by rich donors.
"If you have something to say, say it," Clinton said as she and Sanders met at a debate in New Hampshire that was broadcast on MSNBC.
A fight has been brewing between Sanders and Clinton for days over who is the most genuine progressive after the Vermont senator said that she could not be a moderate and a progressive at the same time. They sparred five days before their next nominating clash, in the New Hampshire primary. A new CNN/WMUR tracking poll published on Thursday showed that Sanders still has a formidable 61% to 30% lead over Clinton among likely primary voters in the Granite State.
The Sanders assault clearly frustrated Clinton, who vociferously defended herself as a progressive who gets results and has spent decades working on children's rights and health care.
"I am not making promises that I can't keep," she said.
Clinton said that by Sanders' definition of progressive politics, there would be nobody left in the movement, including President Barack Obama, Vice President Joe Biden and the late Sen. Paul Wellstone, who was a hero to liberals.
"I don't think it was particularly progressive to vote against the Brady bill five times," Clinton said, referring to past votes by Sanders on gun control.
Sanders hit back by pointing out that Clinton had referred to herself as a moderate at an event in Ohio last year. And he said that Obama and Biden had done a "fantastic job" pulling America back from the Great Recession.
"Do I think President Obama is a progressive? Yes, I do," Sanders said, though he added that he disagreed with the President on the Trans-Pacific Partnership trade pact.
Sanders billed himself as the true outsider candidate in the race, while suggesting that Clinton was the candidate of the establishment. He argued that she would never be able to get money out of politics because she has a multimillion-dollar super PAC.
At one point, as their tempers started to flare, Clinton and Sanders spoke over the top of one another as they sparred over the definition of progressive politics.
"Instead of arguing about definitions, let's talk about what we should do (as president)," Sanders said.
Clinton shot back: "You began it yesterday with your comments," referring to Sanders questioning her progressive credentials at Wednesday's CNN town hall.
Clinton wasn't the only one to show anger during the debate.
Sanders delivered a characteristically loud performance, directing his own anger at Wall Street, which he described as an "entity of unbelievable economic and political power."
When the debate turned to foreign policy, Clinton found a new way to deflect criticism over her 2002 vote to authorize the war in Iraq, which has haunted her political career ever since.
"A vote in 2002 is not a plan to defeat ISIS," Clinton told Sanders, arguing that it is now more important to defeat the terror group that has taken over vast areas of Iraq and Syria than continue to argue about the roots of the Iraq War.
Sanders countered that the decision on whether to wage war on Iraq was a question of judgment and recalled that he cast an opposite vote to Clinton's while he was a member of the House.
Clinton, meanwhile, was asked to reassure Democratic voters that the FBI inquiry into the private email server that she used as secretary of state would not lead to damaging revelations on her conduct and handling of classified information that could blow up her campaign if she is the party's presidential nominee.
"I have absolutely no concerns about it whatsoever," Clinton said. "I am 100% confident."
Sanders refused to take the opportunity to criticize Clinton over the email issue.
After the debate, the Clinton campaign blasted Sanders on foreign policy, accusing him of drawing a clumsy comparison between the U.S. policy of opening diplomatic relations with Cuba and the proper way to approach Iran, which remains locked in confrontation with Washington despite the clinching of a nuclear deal last year.
Clinton campaign manager Robby Mook told CNN's Don Lemon that Clinton has shown herself able to handle both domestic policy and to serve as commander in chief.
"I think you saw Sen. Sanders fail that national security test," Mook said.
But Jeff Weaver, who is Sanders' campaign manager, said that much of the debate unfolded on issues that his candidate had introduced in the campaign -- namely the influence of big money in politics.
And he denied that Sanders was guilty of an underhand smear against Clinton.
"These big companies that give all this big money don't do it just out of the goodness of their heart, they are thinking they are getting something back for it," Weaver told Lemon.