Sanders ignited a new burst of worries with an appearance on “60 Minutes," in which he defended his previous praise of Fidel Castro’s Cuba regime and brushed off questions about the costs of his proposals. This raised concerns about Sanders’s history of sympathy for communist and socialist regimes, and how Republicans might use that against him in a general election.

The interview, which drew sharp pushback from Florida Democrats, also raised questions about whether down-ballot Democrats — particularly those in tough states and districts — might see his past positions and more ambitious policies as politically perilous for them, and whether Sanders even sees that as a problem.

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Sanders also regularly bashes the Democratic establishment, which suggests he might struggle to unify the party behind him as nominee, though both sides will have an obligation to make that happen.

Opinion Who could win the Democratic primary? Use the Post Opinions Simulator to pick a state and see what might happen in upcoming primaries and caucuses.

I asked Ben Tulchin, the pollster for the Sanders campaign, to respond to these worries. A lightly edited and condensed transcript of our conversation follows.

Greg Sargent: What does Sanders’s winning coalition in November look like?

Ben Tulchin: If he wins the nomination, he will have a unified Democratic Party behind him, based on strong antipathy towards Donald Trump. That gives us a solid, very motivated base.

He does several points better than any other Democrat against Trump among 18-to-34 year-olds, which is a significant percentage of the electorate.

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Bernie has consistently done better among independents than any other Democrat tested, particularly younger independents, which is an important part of Bernie’s base, especially younger independent men.

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College-educated Democrats are going to be solidly with us, because they rabidly hate Trump. Young voters, independents, Latinos — look at the overwhelming margin Bernie won Latinos by in Nevada. That puts him in a position to put Texas in play. There’s a small but fast-growing Latino population in North Carolina. Bernie could do well with Latinos in Florida.

Sargent: One of Barack Obama’s alumni said on TV that for Bernie, Florida, North Carolina, Arizona and Georgia are basically off the table. You reject that?

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Tulchin: Absolutely. Bernie is the most popular of all the Democratic candidates running. If our base is unified, Bernie can bring segments of the electorate to the table better than other Democrats: young voters, Latinos, independents. Bernie does particularly well for Democrats with white working-class voters, particularly younger working-class white men.

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Bernie has strong appeal with working-class voters regardless of ethnicity — white, Latinos, African Americans.

Sargent: About the 2018 elections: We saw the highest midterm turnout in a century, and an 8-to-9-point national popular-vote win for Democrats. Yet a lot of that was driven by a suburban shift — in college-educated and suburban whites.

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It often seems to me that the way Bernie talks embodies a take on national politics that overlooks that election. What do you take from it?

Tulchin: It points to a very motivated Democratic base. I see that momentum carrying through to 2020. Bernie’s core message of taking on the one percent and the system is even more applicable today, because we have the perfect poster child of that system in the White House.

Trump inherited his wealth, doesn’t pay his fair share of taxes, gives himself and his billionaire cronies a tax cut while trying to take health care from millions of working people.

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Bernie can stand toe to toe with Trump and say, “You represent the rigged economy and corrupt political system.”

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Sargent: I want to press you on 2018. That win was driven by a galvanized Democratic base. But it was also driven by a big shift in the suburbs and among educated whites. I want to understand the degree to which you see holding those gains as crucial to winning in 2020.

Tulchin: The key to that is making the election a referendum on Donald Trump. [He] is uniquely polarizing, sexist, racist, misogynist. That motivates suburban voters. Bernie is solid on all the social issues they care about, especially choice.

But we can’t just rely on that suburban vote. Bernie has unique appeal with working-class voters. He can be more effective in Michigan, Wisconsin and Pennsylvania. If we turn just those three states around, we win the White House.

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These suburban voters hate Trump. They’ll vote for the Democrat. Bernie can add to that coalition.

Sargent: One plausible interpretation of these big shifts among suburban and educated whites is that a fairly anodyne message on health care and immigration is precisely what allowed Trump’s efforts to take health care away from people and his caging of children to work against him.

Do things like Medicare-for-all and a much more progressive position on immigration risk costing those voters?

Tulchin: In our polling, when we push back on arguments against Medicare-for-all, we win by 20 points, because it’s an argument over who do you trust on health care: Sanders, who will set you up with affordable health care under a Medicare-for-all system, or Trump and Republicans, who spent years trying to take health care away? That’s a debate I welcome.

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Sargent: There will be hundreds of millions of dollars in ads arguing that under Bernie’s plan, private insurance will be done away with. How deep is the concern is about that?

Tulchin: It’s not a one-sided argument. If Bernie is the nominee, we’ll have money on our side to make our case. That’s what our polling did, and we won by 20 points. The reason is voters trust us generally on health care.

This isn’t an isolated issue. It’s tied to the broader argument that Bernie stands up for working people, and Trump is representing the billionaire class. Medicare-for-all fits into that frame.

Sargent: It often does seem that the details of policy disputes matter less than voter perceptions of whether the candidates are in some fundamental sense on their side or not.

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Tulchin: It’s about who you believe on health care: The guy who wants to provide affordable health care to everybody? Or the guy who has been trying to take health care away from people?

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Sargent: The other day, Bernie tweeted that the Republican establishment can’t stop him, and the Democratic establishment can’t stop him. Some Democrats hear that and ask themselves whether Bernie’s instinct as nominee would be to say, “We can do this without the establishment. We’re running our own movement."

Tulchin: Bernie’s speech after Nevada was a good indication of his ability to reach out and bring the party together. Trump is the best unifying force for the Democratic Party. We’re going to stay together because we all are highly motivated to beat Trump.

We’re in the middle of a primary battle. Remember 2008, the throes of the Obama-Clinton battle? No one thought the party could come together after that. We won the White House.

Sargent: Bernie’s rhetoric is sometimes more unifying than he gets credit for.

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Let me ask you about House members in front-line districts. On “60 Minutes,” the way he responded to the Castro quote was interesting. He was unapologetic and immediately pivoted to awful quotes from Trump about various dictators.

You already saw one House member in Florida condemn it anyway. There’s a whole wealth of other quotes about communist and socialist regimes out there. To what degree to you recognize the difficulty that some of this might impose on Democrats in tough places?

Tulchin: People have seen him on the national scene for five years now. He’s seen as honest, has integrity, cares about people like them.

Voters have a good sense of who he is and what he’s about. There will be a lot of stuff said against him. But when you have real positive attributes, and a huge advantage over Trump on many of them, we’re going to be in a position to overcome any negative information thrown his way.

He does well in rural and white working-class districts where Democrats have struggled. Bernie brings something different to the mix that can actually put more districts in play. There’s an upside to him that’s getting discounted right now.

Sargent: Another way to put that is he could start to reverse the realignment we’ve seen under Trump along education lines among white voters.

Tulchin: Correct. He could restore lost ground.

Sargent: When you hear a member like that in Florida denounce a quote like this, what do you take from that? Is it something Bernie needs to worry about, or not?

Tulchin: Win the nomination, and unify the party. Once you unify the party, you make Trump the focus.

The good news is that Trump has one of the weakest job approval numbers in history. He’s got highly unpopular personal favorability ratings. And Bernie has a lot of strengths that contrast well with Trump.