The Bernie Bros are vowing revenge.

As the presidential campaign of Sen. Bernie Sanders continues to crash and burn, the socialist’s most hard-core supporters are vowing they will never vote for Joe Biden at the ballot box — even if that means handing Trump a second term.

“We will never – NEVER boost or support Joe Biden or defend his abysmal record and terrible policy positions,” Henry Williams, executive director of The Gravel Institute, told The Post. “We will tell people, as we always have, to vote their conscience and to make decisions based on the interests of all the world’s oppressed people … I do expect a massive exodus from the Democratic Party.”

Williams, along with David Oks and Henry Magowan, are the driving forces behind the brief presidential campaign of Mike Gravel, an 89-year-old former Alaska senator who left the race in August. The trio then became enthusiastic Bernie Bros.

“I don’t know if I could vote for Biden,” said a high-profile local Democratic Socialist. “Biden is just an old white guy who inspires nobody. I sincerely think he will lose the electoral and popular vote and I know I won’t be voting for him in New York.”

The grumbling from Sanders die-hards is no idle threat. A whopping 12% of them voted for Trump in 2016, according to an analysis by Cooperative Congressional Election Study. That added up to roughly 216,000 voters in Michigan, Pennsylvania and Wisconsin, exit polls showed. Trump’s combined margin of victory in those states was 77,744.

An untold number of additional Sanders fans almost certainly stayed home or voted third party in 2016 in an election plagued by low turnout on both sides. Green Party candidate Jill Stein earned more votes in each rust-belt battleground than the margin separating Trump from Hillary Clinton. One of those Jill Stein voters was Briahna Joy Gray — Sanders’ current campaign spokesperson.

Other Bernie Bros are attempting to split the difference, urging comrades to bolt from Biden in safe states, but hold their nose and pull the lever for him in the swings.

“I have seen a whole lot of people who live in Wisconsin or live in a state like Pennsylvania who feel very obligated to vote for whoever the [Democratic] nominee is because they’re just thinking it’s a zero sum game,” Sam Finkelstein, a law student at Seton Hall University and ferocious Twitter Bernie Bro told The Post.

An aide to Biden insisted that his strength with other demographics would more than offset renegade Bros, but told the Post they recognized the challenge and were prepared for outreach.

“It is going to be our job to bring the party together and reach out to everyone and create a united front,” the aide said.

After sweeping to victories in the early states, many believed Sanders was on a glide path to the Democratic nomination. The momentum was halted by Biden after a crushing victory in South Carolina and strong showings on Super Tuesday. Former establishment rivals like Amy Klobuchar, Pete Buttigieg and Mike Bloomberg quickly consolidated around the former vice president. Now, far behind in the delegate math, it’s Sanders who finds his campaign on life-support.

Though party bosses have been agonizing over how to nudge the 78-year-old socialist out of the race, his cheerleaders say the senator should fight on — at least through Sunday’s debate and another round of voting Tuesday — and potentially even further. In 2016, Sanders soldiered into June and only endorsed Hillary Clinton in July, inhibiting her consolidation of the party.

“I think staying in the race is the responsible thing to do,” Bhaskar Sunkara, founder and editor of the socialist magazine Jacobin told The Post. “He needs to challenge Biden on certain aspects of his rhetoric. He needs to accumulate clout and delegates to shape the Democratic platform and pressure the Biden campaign into adopting a more popular economic platform.”

Sunkara says he too has no plans to vote for Biden.