These Democrats are feeling Berned out.

Democratic donors and party insiders are warning that large swaths of their voters could stay home — or even defect to Trump — if Vermont Sen. Bernie Sanders snags the nomination.

“I’ll still put a Bernie Sanders bumper sticker on my car, but a lot of people won’t,” said Jim Kessler, executive vice president for policy at Third Way, a Democratic think tank not aligned with any candidate. “They’ll say ‘I don’t like Donald Trump, but I don’t like Sanders either. We survived four years of Trump, maybe we’ll survive another four years.’ They’ll stay home, vote third party, or vote for Trump.”

An insider working with Mike Bloomberg’s campaign agreed: “I think that there is a very real ‘Never Bernie’ sentiment amongst both the donor class and moderate, centrist Democrats, or what I would call regular Democrats. Bloomberg and Pete [Buttigieg] and [Joe] Biden, who represent the heart and soul of the party — their supporters are not as apt to support someone like Bernie.”

After an October heart attack left many assuming Sanders’ candidacy was DOA, the 78-year-old socialist has bounced back. A new Iowa State University poll found 24 percent of Iowa voters behind him, with Massachusetts Sen. Elizabeth Warren at 19 percent; former South Bend, Ind. Mayor Buttigieg at 17 percent and former VP Biden at 15 percent. In New Hampshire, another recent poll gave Sanders a 15-point lead.

This has led to alarm bells among establishment Democrats, one of whom said Jeremy Corbyn’s Labour Party blowout in England to Boris Johnson was a warning shot.

Among insiders there is near-universal belief that Sanders’ card carrying socialist credentials could create enormous problems with suburban and older voters — both of whom tend to be wealthier than the general population. While millennials are evenly split between socialism or capitalism, only 39 percent of Generation Xers and 32 percent of Baby Boomers held favorable views of “socialism,” according to a November 2019 Gallup poll.

Sanders was the first socialist elected to Congress in decades when he arrived as a freshman Representative in 1991. He moved up to the Senate in 2007. He has always worn the baggage — like past praise for Fidel Castro, and his Soviet honeymoon — on his sleeve. With few major legislative achievements, he was largely dismissed as a Senate sideshow — until his breakout performance in the 2016 Democratic primary.

“For Democrats to win, the election must be a referendum on Trump and not a debate about socialism,” Michael Kempner, a longtime Democratic donor who has cut checks for Biden and Buttigieg, told The Post. “The vast majority of Democrats and the nation do not believe in socialism.”

The rumblings appears grassroots for now. Multiple party grandees contacted by The Post insisted there was no organized “Never Bernie” movement — and they would honor pledges to support whoever ended up on top of the ticket.

“There’s nothing coming from the DNC, party leaders or those who are in the loop. Donors get moody all the time,” former DNC chair Donna Brazile told The Post.

The establishment assurances, however, have been muddled by Hillary Clinton. She refused to commit to Sanders’ candidacy, telling the Hollywood Reporter last month she’s “not going to go there yet.” She later put out a statement saying she would support whoever the nominee was.

News also emerged Friday of DNC members privately discussing rules to prevent a Sanders nomination at the Democratic convention, according to Politico.

Brazile herself famously leaked debate questions to Hillary Clinton in an effort to tilt the scales in her favor against Sanders in 2016, and has long been viewed with suspicion by progressive diehards. After Clinton clinched the nomination — Sanders’ supporters were told they needed to fall into line and support the nominee — something they have not forgotten.

A person close to Sanders campaign told The Post, they were aware of the “Never Bernie” effect, but unbothered.

“There’s no point in being afraid of it. You see it and try to work to overcome it,” said the insider.

Sanders campaign spokesperson Briahna Joy Gray did not respond to request for comment.