He responded by listing a number of policy proposals, from raising the minimum wage to $15 an hour to making community college tuition free, and asked the audience to shout out if they thought they were too "extreme."

"I live, Jane [my wife] and I, live 50 miles from the Canadian border," he said. "Somehow they manage to guarantee health care for every man and women and child in their country at half the cost we spend per capita. Is guaranteeing health care as a human right a radical idea?"

The crowd responded with resounding no's.

"This is a scientific poll, you hearing this?" Sanders said, jokingly, to CNN's Chris Cuomo.

"I rest my case," Sanders eventually added.

Cuomo, who was moderating the event, brought up Democratic rival Pete Buttigieg's past remarks that Sanders was not only extreme in his ideas, but also polarizing. Cuomo asked Sanders to respond to possible concerns that he would be difficult to work with, and the Vermont senator rebuffed that as "nonsense."

Sanders cited his years in Congress getting legislation passed with members of both parties and shot back at Buttigieg saying his "ideology may be shaped from raising a lot of money from 40 or 45 billionaires."

Later in the evening in his own CNN town hall, Buttigieg stood by his remarks on Sanders, claiming that most Democrats are not on board for many of Sanders' policies. Buttigieg said that it is far more important than ever that Democrats win this election and that his message of appeal to moderates and seasoned Democrats alike would win in November.

"We have to be building a kind of politics that's about that inclusivity victory, not about rigid ideology."

Sanders also said defeating Trump was a top priority for the Democrats and that he would hope all candidates in the field would back whichever challenger ultimately got the nomination. He said to failure to do so would be destructive.

"If one candidate comes out on top, to say to the country ... by the way we don’t think that candidate should be the nominee, I think that should be a serious, serious problem for the Democratic Party, and I think that would wreck havoc on that person's campaign," he said.

Sanders has come under scrutiny for the tactics of some of his supporters in antagonizing other Democrats and using abusive language online. Buttigieg came after Sanders during the last Democratic primary debate for not doing more to disavow the online bullying.

During Monday's town hall in Charleston, Sanders firmly turned his back on supporters engaged in malicious behavior, saying: "We don’t want your support if you think that our campaign is about making ugly attacks on other candidates."

"We have millions of followers," Sanders said. "I’m not going to tell you that we don’t have some jerks out there."