At a CNN town hall in Derry, New Hampshire, ahead of next Tuesday's first-in-the-nation primary, Sanders slammed Clinton, arguing that she's out of step with the party's base on issues ranging from campaign finance to climate change, trade and the Iraq War.
"I do not know any progressive who has a super PAC and takes $15 million from Wall Street," Sanders told CNN moderator Anderson Cooper. "That's just not progressive. As I mentioned earlier, the key foreign policy vote of modern American history was the war in Iraq. The progressive community was pretty united in saying, 'Don't listen to Bush. Don't go to war.' Secretary Clinton voted to go to war."
Clinton shot back in her session following Sanders, quipping that she was "amused" that the Vermont senator appears to consider himself the "gatekeeper on who's progressive."
"So I'm not going to let that bother me," she said. "I know where I stand."
Tension between Clinton, Sanders
The exchange captured the tension that is building between Clinton and Sanders ahead of the primary. Since Monday night's Iowa caucuses, which Clinton very narrowly won, the two have volleyed sharp words over the ideological direction of the Democratic Party in the post-Barack Obama era. The race, however, isn't nearly as negative as the Republican primary contest, which was dominated on Wednesday by personal attacks between Donald Trump, Ted Cruz and Ben Carson.
Clinton delivered an uneven performance at the event, sounding confident on policy answers and connecting with the audience when she shared moments from her personal life but stumbling on topics that have dogged her throughout the campaign, including her vote on the Iraq War and her relationship with Wall Street.
Her toughest moment of the night came when she was asked to address the paid speeches she gave at Goldman Sachs after leaving the State Department.
Clinton started to explain that Goldman wasn't the only group that paid her for speeches. But when Cooper interjected and asked, "Did you have to be paid $675,000?" Clinton appeared caught off guard.
"Well, I don't know. Um, that's what they offered," she said. Clinton went on to insist that at the time of the speeches, she was undecided on whether to seek the White House.
"I didn't know, to be honest, I wasn't -- I wasn't committed to running," Clinton said, uncharacteristically tripping over her words. "I didn't -- I didn't know whether I was running or not. I didn't."
And in one of the more revealing exchanges of the night, Cooper asked Clinton what would be wrong with the so-called "political revolution" that Sanders frequent calls for. Clinton paused before responding: "That's for Sen. Sanders to explain."
'Vast right-wing conspiracy'
Asked about one of her most famous quotes from the 1990s, Clinton said she still believes that there is a "vast right-wing conspiracy."
"Don't you?" she asked Cooper. "It's gotten even better funded. They brought in some new multi-millionaires to pump the money in."
The 60 minutes Clinton stood on stage also confirmed, once again, that her vote for the Iraq War continues to haunt her 13 years later.
One woman who was chosen to ask a question praised Clinton for her foreign policy experience, but said: "I get stuck when I think about you voted for the Iraq war, which you now say was a mistake."
"What have you learned since that vote that could give me confidence that you wouldn't make a mistake of that magnitude again?" she said.
"I think that's a very fair question," Clinton responded. "I did make a mistake and I admitted that I made a mistake."
Meanwhile, Sanders, a self-proclaimed democratic socialist, found himself defending his own credentials as a member of the Democratic Party, noting that the party's leadership on Capitol Hill has placed him in high-ranking positions on congressional committees."Of course I am a Democrat and running for the Democratic nomination," he said.
Sanders pushed back on the suggestion that Clinton is a better general-election candidate than he would be. The senator, who has drawn massive crowds to his campaign rallies and has somewhat of a cult following among younger voters, said history shows that Democrats win elections when there is large voter turnout.
There is simply more enthusiasm fueling his campaign than Clinton's, he said.
'Excitement and energy'
"An objective assessment," Sanders argued, "would say there is more excitement and energy in our campaign."
He also took a shot at Trump, calling him a candidate who doesn't support working Americans. But as much as Sanders doesn't like the Republican's agenda, the senator said he would delight in taking him on in November.
"I want Trump to win the Republican nomination and I would love the opportunity to run against him," he said. "I think we would win by a lot."
Trump quickly responded with a swipe at Sanders on Twitter.
"Sanders says he wants to run against me because he doesn't want to run against me," Trump said. "He would be so easy to beat!"
Polls in New Hampshire suggest the primary will not be as close as the nail-biting Democratic caucuses in Iowa. Sanders, riding his high favorability in a state that borders his stomping ground of Vermont, has a strong advantage, leading Clinton 55% to 37% in the latest CNN Poll of Polls.
Still, Sanders insisted that he's the underdog in the Democratic race despite his commanding lead in New Hampshire polls.
"Of course we're an underdog. We are taking on the most powerful political organization in the country," Sanders told Cooper in another clear swipe at Clinton. "We started this campaign nationally, as you well know, 40, 50, points behind Secretary Clinton ... I think it's fair to say we have come a pretty long way in the last nine months."