CHARLESTON, S.C. — As President Trump fixates on former Vice President Joe Biden as his opponent in the 2020 general election, some moderate Democrats are more afraid of Bernie Sanders becoming the eventual nominee.

Driving the news: A two-day conference hosted here by the centrist Democratic group Third Way focused on helping Democrats figure out "the way to win" in 2020 — and they're sick of economic messages that focus on "free stuff" rather than opportunity, as former North Dakota Sen. Heidi Heitkamp put it.

They're not down with Medicare for All, and shared data to back up their fear. Among 1,291 Democratic primary voters polled by Third Way, there's a 17-point difference in support for Medicare for All between "Twitter Democrats" and Democratic primary voters as a whole.

In fact, they'd love if all the 2020 Democrats got off Twitter entirely. Listening to the Twitterverse "will help re-elect Donald Trump," according to Lanae Erickson, Third Way's SVP for social policy and politics.

They're also trying to obliterate the "blue bubble" created by liberals — perpetuated, they say, by appearances on networks like MSNBC and an obsession with online reach. "If you killed it on that podcast, I assure you we did not hear you," said Steve Benjamin, mayor of Columbia, S.C.

Things like free college are "fluffy" and perceived as "handouts," said Anna Tovar, mayor of Tolleson, Arizona. Particularly with Latinx Democrats, she said, "They want to work towards [those opportunities] and be proud of that."

Yes, but: Many of the serious 2020 Democratic contenders are calling for and engaging with the things they decry — so the problem is bigger than Bernie.

But Elizabeth Warren — who’s viewed as the closest candidate to Bernie ideologically — gets a pass with these moderates. They say she’s focused on a Democratic capitalist message, while they view Bernie as a full-blown socialist.

What they're saying: These things are politically potent for Republicans. "We shouldn't be running on these ideas; we should be running from them," said Jon Cowan, Third Way's president.

Be smart: President Trump will label any of the candidates a Democratic socialist, to varying degrees of success, but these folks are adamant anyone but Bernie can win: a gay mayor; an African American woman; a Latino from Texas; a former vice president.

"But I don't believe a self-described Democratic socialist can beat Donald Trump," said Cowan.

The bottom line: Expect the tension between liberals and centrists within the Democratic party to grow even more as these issues (Medicare for All, the Green New Deal, etc.) get prime airtime at the debates.

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