Bernie Sanders had an impressive win last night in the Nevada caucuses. He also won in the New Hampshire primary and leads the Democratic field in national polls. It's a stunning turn of events for a man who calls himself a "democratic socialist," and is the first to admit he's been preaching the same populist, progressive message for decades.

As the mayor of Burlington, Vermont, then a U.S. congressman, now an independent senator who caucuses with the Democrats, Sanders has been arguing that the very rich should pay higher taxes so that everyone can have health care, education, and a decent paying job. Sanders is 78 years old, and is filling arenas with huge crowds of young, enthusiastic supporters. He's used to being the underdog, but now, grudgingly, has to admit: in the Democratic race for president, he's the front-runner.

Bernie Sanders

Anderson Cooper: After your entire career, to now be the front-runner of the Democratic Party--

Bernie Sanders: Yes, that is a bit shocking. I will agree. I will agree with you there.

Anderson Cooper: The Democratic Party has moved to you, if anything?

Bernie Sanders: In many ways, they have. And-- and the ideas that seemed radical four years ago are now kind of mainstream.

Anderson Cooper: The ideas are still pretty radical. I mean you've been saying with pride that you're making a lot of people nervous. You said, "Wall Street's getting nervous, the insurance industry's getting nervous, drug companies are getting nervous, and the Democratic establishment is getting nervous."

Bernie Sanders: Yep, that's what I said.

Bernie Sanders at a rally: You know what? They should be getting nervous!

Anderson Cooper: You're also making, though, a lot of Democratic voters nervous.

Bernie Sanders: I don't think so. I-- look, you know, you have a lot of candidates out there. And each candidate has his or her supporters.

Anderson Cooper: But a lot of voters are voting for candidates who aren't calling for Medicare for All, who aren't calling for a revolution. Is everybody really wanting a revolution like that?

Bernie Sanders: Yeah, let's go easy on the word rev-- "political revolution", you know? We're-- we're trying to follow--

Anderson Cooper: Y-- you're the one who's using the word.

Bernie Sanders: Well, I mean, you know, but I don't want people, you know, to overstate that. But here is the point. It's not good enough to complain, "Oh, I cannot afford my health care. I can't afford childcare. I can't afford to send my kid to college. I'm paying half of my income in rent." You know? If you're not happy about that, you got to be involved in the political process. Only millions of people standing up for justice can bring about the kind of change that this country requires. And I believe that has got to happen.

Sanders waves to supporters at a campaign rally on February 21, 2020, in Las Vegas, Nevada. Getty

Sanders says the change he envisions most closely resembles Scandanavian and European countries with democratic governments and comprehensive social programs. But that's certainly not how President Trump has characterized it.

And it's not just President Trump. At the debate this past week in Las Vegas, this is how former New York Mayor Michael Bloomberg responded to one of Sanders' proposals to require greater employee ownership of large companies.

Michael Bloomberg: I can't think of a way that would make it easier for Donald Trump to get re-elected than listening to this conversation. This is ridiculous. We're not going to throw out capitalism. We tried that. Other countries tried that. It was called communism. And it just didn't work.

Anderson Cooper: You said it was a cheap shot that he said that. What's going to happen on the stage w-- with President Trump, he's going to be doing shots all the time on you, on this.

Bernie Sanders: And you know what? We will fight back. And this is what we will bring up. We will bring up is that the president of the United States is a pathological liar. And it is increasingly clear that many people just don't believe anything that he says. He is a fraud. I look forward to taking him on.

Anderson Cooper: What is democratic socialism?

Bernie Sanders: When Donald Trump was a private businessman in New York, he got $800 million in tax breaks and subsidies to build luxury housing. That's called corporate socialism. What democratic socialism is about is saying, 'Let's use the federal government to protect the interests of working families.'

Back in the 1980s, Sanders had some positive things to say about the former Soviet Union and the Sandinistas in Nicaragua.

Here he is explaining why the Cuban people didn't rise up and help the U.S. overthrow Cuban leader Fidel Castro: "…he educated their kids, gave them health care, totally transformed the society, you know?"

Bernie Sanders: We're very opposed to the authoritarian nature of Cuba but you know, it's unfair to simply say everything is bad. You know? When Fidel Castro came into office, you know what he did? He had a massive literacy program. Is that a bad thing? Even though Fidel Castro did it?

Anderson Cooper: A lot of p-- dissidents imprisoned in-- in Cuba.

Bernie Sanders: That's right. And we condemn that. Unlike Donald Trump, let's be clear, you want to-- I do not think that Kim Jong Un is a good friend. I don't trade love letters with a murdering dictator. Vladimir Putin, not a great friend of mine.

Sanders arrives, flanked by his wife Jane O'Meara Sanders, to speak at a Primary Night event at the SNHU Field House in Manchester, New Hampshire, on Tuesday, February 11, 2020. Getty

A month ago, Sanders was told by U.S. intelligence that Vladimir Putin's government has been attempting to help his campaign. And last week, lawmakers were briefed that Moscow is also trying to help re-elect President Trump. On Friday, Sanders offered this message to Putin: "As president of the United States, Mr. Putin, you will not interfere in our elections.''

Anderson Cooper: You believe winning absolutely relies on a voter turnout that this country's never seen before?

Bernie Sanders: That's right. I-- I think-- look, anyone who tells you that Donald Trump is not gonna be a tough opponent is kidding themselves. The way you beat Trump is bring nontraditional voters into the political process.

Anderson Cooper: Donald Trump got elected talking to white middle-class Americans, white working-class Americans, promising to-- to make America great again. Your stump speech, your critics say sounds like nothing works in America, hasn't for generations. Is America great?

Bernie Sanders: In many ways, we are. In some ways, very significant ways, we're not. We're not great when half of our people today are living paycheck to paycheck. When 500,000 people tonight are going to be sleeping out on the streets, including 30,000 veterans. You know, my father came to this country at the age of 17 without a nickel in his pocket. Couldn't speak a word of English, had very limited education. We are a great nation, because people like my father would never have dreamed in a million years that their kids would become United States senators or be successful in many other ways.

Sanders speaks at town hall at the National Motorcycle Museum on January 3, 2020, in Anamosa, Iowa. Getty

Anderson Cooper: How much of your political beliefs are based on your experiences growing up in Brooklyn-- with your family?

Bernie Sanders: A lot, Anderson, a lot. I grew up-- and I don't want to hear-- anyone to think I'm-- we were desperately poor. We were not. My father worked every day of his life. He worked very hard, just never made a whole lot of money. And, you know, as a kid, this stays with you your whole life. These are the things you don't forget. The incredible arguments between my mom and my dad-- over money-- you know? Why didn't we have enough money to do this? And should we buy this and do that? And why are you buying this clothing? And bah bah bah bah.

Anderson Cooper: Your mom got sick when you were a teenager.

Bernie Sanders: Mhmm.

Anderson Cooper: Does that inform your view on medical policy, on Medicare for All, and all of that?

Bernie Sanders: I don't like to, you know, talk about personal stuff that much. But it does.

Anderson Cooper: It's interesting you don't like to talk a lot about personal stuff. Most people running on a campaign, they want people to know that side of them. Why do you think that's not important?

Bernie Sanders: I'm not saying that's not important. I'm a kind of-- private person in a sense. And I-- and I-- you know, I'm not particularly anxious to tell the world about everything personal in my life.

Anderson Cooper: One of the things obviously people do know about is you had a heart attack a few months ago. If-- if you're elected, running for a second term, you'd be 82 years old. Somebody running for a second term at 82, shouldn't that give voters pause?

Bernie Sanders: Well, I haven't won the first term yet, so let's--we'll see what happens on the second term. Being old has an advantage in the sense that the issues that I fight for are not new to me.

Anderson Cooper: One of the criticisms of you in the Senate, Joe Biden has said that you never got anything done.

Bernie Sanders: Pssst

Anderson Cooper: Amy Klobuchar has been-- are you getting mad?

Bernie Sanders: I'm not mad– just silently hissing, that's all. (LAUGH)

Anderson Cooper: Amy Klobuchar says to be a progressive, you need to make progress, implying you haven't. A Georgetown University study that you had one of the worst records for bipartisan cooperation in the Senate.

Bernie Sanders: Oh boy, dead wrong, dead wrong, dead wrong. When I was in the House, year after year after year, I passed more bipartisan amendments than anybody else in the House.

Anderson Cooper: In terms of getting your bills through Congress, we found, I think, what, seven bills that you were the primary sponsor on that got enacted. Two of them were-- involved naming Post Office buildings.

Bernie Sanders: Yeah, but if you look at the Affordable Care Act, my name was not on that bill. But you speak to anybody in Congress, I led the effort to bring $11 billion more into community health centers and expand-- primary health care in this country. I mean, the-- as you well know, Anderson, Congress is a complicated place.

There's profound skepticism in Congress about Sanders' ability to get his agenda passed. Two-thirds of Democrats in the Senate have not signed on to "Medicare for All," which would cost an estimated $30 trillion to $40 trillion over ten years. And that's just one of Bernie Sanders' many proposals. There's also free public college, cancellation of all student debt, a federal job guarantee, and a Green New Deal to rapidly reduce carbon emissions.

Anderson Cooper: How much will that cost?

Bernie Sanders: Obviously, those are expensive propositions, but we have done our best on issue after issue-- in paying for them.

Anderson Cooper: Do you know how all-- how much though? I mean, do you have a price tag for-- for all of this?

Bernie Sanders: We do. I mean, you know, and-- and-- the price tag is-- it will be substantially less than letting the current system go. I think it's about $30 trillion.

Anderson Cooper: That's just for Medicare for All, you're talking about?

Bernie Sanders: That's just Medicare for All, yes.

Anderson Cooper: Do you have-- a price tag for all of these things?

Bernie Sanders: No, I don't. We try to-- no, you mentioned making public colleges and universities tuition free and cancelling all student debt, that's correct. That's what I want to do. We pay for that through a modest tax on Wall Street speculation.

Anderson Cooper: But you say you don't know what the total price is, but you know how it's gonna be paid for. How do you know it's gonna be paid for if you don't know how much the price is?

Bernie Sanders: Well, I can't-- you know, I can't rattle off to you ever nickel and every dime. But we have accounted for-- you-- you talked about Medicare for All. We have options out there that will pay for it.

Vermont Senator Bernie Sanders gestures during the sixth Democratic primary debate in Los Angeles on December 19, 2019. Getty

Taxes on corporations and billionaires are the primary options he's proposed. But to finance Medicare for All, middle-class families would also pay an additional 4% tax on their income over $29,000. Sanders says they'll end up saving money because they won't have to pay premiums, co-pays, or deductibles. But under Medicare for All, nearly 160 million Americans will have to give up their private health insurance.

Anderson Cooper: Isn't that a dangerous message for Democrats to say, "You know what? We're gonna take away your private insurance. We're-- we're gonna give you something better--"

Bernie Sanders: Let's talk about--

Anderson Cooper: "--run by the government." A lot of people don't trust that.

Bernie Sanders: It's not run by the government. Medicare allows you to go to any doctor you want for better or worse, this is not socialized medicine. This is keeping the same system intact, but getting rid of the private insurance companies, giving people another card, which allows them complete freedom.

Though he's campaigning as a champion for the poor, Bernie Sanders became a millionaire four years ago, thanks largely to royalties from his bestselling book, "Our Revolution." His Democratic rivals have given him some grief about it during the debates.

Anderson Cooper: You know what they're getting at. They're-- they're suggesting the it's hypocritical, it's criticism--

Bernie Sanders: We pay our fair share of taxes.

He doesn't think billionaires like Michael Bloomberg are paying their fair share, nor does he think much of the job Bloomberg did as mayor.

Bernie Sanders: I think the more people understand Bloomberg's record as mayor of New York, where he engaged in horrifically racist policies of stop and frisk, people in America don't want that.

Anderson Cooper: You have promised to support the Democratic nominee. Personally, though, the idea of you going out campaigning for Michael Bloomberg, a billionaire, how would that even work?

Bernie Sanders: I--

Anderson Cooper: I mean can you honestly tell your supporters to support--

Bernie Sanders: Well, I-- I think this is the problem of a Bloomberg candidacy. It's not just my supporters, he is not going to be a strong candidate. But, what I have said, and you quoted me correctly, is I said on day one I will support the Democratic nominee, no matter who that nominee may be.

At the end of our interview, Sanders unveiled a new plan that would guarantee free, high-quality child care and pre-kindergarten to every kid in the country from infancy to age four.

Bernie Sanders: So what we are calling for is universal childcare.

Anderson Cooper: How are you going to pay for this?

Bernie Sanders: We have a tax on wealth to pay for that.

Anderson Cooper: For all the people who like the idea of it, there are going to be a lot of Democrats, again, who are saying, "Well, wait a minute, yet again, this is another program that-- it's not clear how it's going to get paid for."

Bernie Sanders: Well, listen--

Anderson Cooper: --it's just going to add to--

Bernie Sanders: It is clear how it's going to be paid for. Look, Anderson--

Anderson Cooper: More taxes.

Bernie Sanders: It's taxes on billionaires. You know? You know, I get a little bit tired of hearing my opponents saying-- "Gee, how you going to pay for a program that impacts and helps children or working-class families or middle-class families? How you going to pay for that?" And yet, where are people saying, "How are you going to pay for over $750 billion on military spending?" How you going to pay for a trillion dollars in tax breaks to the 1% in large corporations which was what Trump did? When you help the billionaires and you help Wall Street, "Hey! Of course we can pay for it. That's what America's supposed to be about." Well, I disagree.

Produced by Andy Court and Evie Salomon. Broadcast associate, Sheena Samu. Edited by Peter M. Berman and Michael Mongulla.