Two days later at a rally in Michigan, Biden endorsed two ideas Sanders pitched at that meeting — expanding Social Security benefits and eliminating medical debt — as goals for “the first 100 days of my second term.” Sanders immediately tweeted his applause.

While conflict over Biden’s candidacy has splintered the Democratic Party, two of its most prominent liberals — Sanders and Rep. Alexandria Ocasio-Cortez (D-N.Y.) — have offered a full-throated defense of the embattled president, providing political cover when he needed it most. In a twist few could have predicted, the two left-wing Democrats have bolstered Biden even as his ideological allies, including former House speaker Nancy Pelosi (D-Calif.), have waffled. “The matter is closed,” Ocasio-Cortez told reporters asking Monday if Biden should step aside.

The endorsements and behind-the-scenes strategizing reflect a careful calculation that Biden offers the best hope for advancing liberal policies — and that such policies offer the best hope for reviving Biden’s political fortunes, according to people close to Sanders and Ocasio-Cortez. The New York Democrat also has spoken privately with White House officials to push for more aggressive government interventions, particularly on housing, a top concern for young voters, according to two other people familiar with the matter, who also spoke on the condition of anonymity to reflect private negotiations.

Ocasio-Cortez reiterated that message directly to Biden in a phone call last weekend, just before she publicly backed him Monday as the party’s nominee, the people said. “Her message to the president was clear: His best shot at winning in November is putting forward an agenda that speaks to the needs of the working class,” said one of the people who was briefed on that call.

A senior Biden adviser played down the idea that Biden is shifting his message in response to these appeals. The president frequently campaigns on such populist policies as reining in prescription drug prices and taxing billionaires. And he endorsed larger Social Security benefits as a candidate four years ago.

“Biden being progressive on economics is not a concession to them — it’s where his heart truly stands,” the adviser said, speaking on the condition of anonymity to candidly discuss the dynamic.

Still, the president’s pledge Friday in Michigan to “end” medical debt if he is reelected marked an expansion of his previous moves to ban medical debt from being considered when people apply for loans and to encourage states to use stimulus funds to forgive medical debt. More than 100 million Americans hold roughly $195 billion in medical debt, according to a 2023 report by Third Way, a Democratic-aligned think tank. And while Biden had previously endorsed expanding Social Security benefits, liberals have long urged him to talk about this plan, as he did Friday.

In a statement, Biden spokesman Charles Lutvak said: “As Michiganders’ support showed last night, Joe Biden is all-in fighting for the middle class — with an ambitious agenda for the first 100 days of his second term that includes pushing to expand and strengthen Social Security by making the wealthy pay their fair share, cancel medical debt and lower rent and home-buying costs.”

Sanders and Ocasio-Cortez are expected to continue pushing Biden to endorse a wider range of their policy positions — a strategy that carries clear risks for both sides.

If Biden loses in November, any policy promises for a second term will be irrelevant. Nationwide, most Democrats want Biden to step aside, according to a Washington Post-ABC News-Ipsos poll. And defections have emerged from Democrats who — unlike Ocasio-Cortez and Sanders — face difficult reelection bids in swing districts or states, with Sens. Jon Tester (Mont.) and Sherrod Brown (Ohio) among those voicing concern.

One adviser to lawmakers on the left, speaking on the condition of anonymity to candidly critique the strategy, said: “If Biden’s not going to be president, what do these concessions really do?”

As for Biden, a majority of voters already see him as “too liberal,” according to a Gallup poll from June. And his biggest political problem has been growing alarm about his mental fitness. In a campaign dominated by Biden’s age and Trump’s criminal conviction and authoritarian tendencies, it’s not clear that any economic policy proposal can move the needle.

Liam Donovan, a GOP strategist, said the endorsements from Sanders and Ocasio-Cortez reflect the reality that any replacement at the top of the Democratic ticket would be less likely to cater to the left than Biden, who has stocked his administration with former staffers to Sen. Elizabeth Warren (D-Mass.).

“The support reflects the fact that Biden has tacked strongly to the left since winning the 2020 primary as an amiable centrist, and any non-Biden alternative is apt to be less aligned with the progressive agenda,” Donovan said.

But while “AOC and company boosting Biden at a perilous moment may help him secure the nomination,” Donovan added, “it doesn’t help him claw back in the Rust Belt states that will decide this election.”

For now at least, Sanders and Ocasio-Cortez appear to be standing firm. Since Democrats lost the House two years ago after failing to pass much of Biden’s Build Back Better agenda, Sanders has pushed Biden to promise the public that material economic benefits would follow if Democrats regain unified control of Washington. He and Ocasio-Cortez also have argued that a long list of liberal policy goals, from expanded Medicare benefits to greater union power, is the best response to widespread voter anger over inflation and the rising cost of living.

“What I think the president does need to do is continue to lean in and move further toward the working class, and be more assertive in providing an affirmative vision for this country,” Ocasio-Cortez told reporters outside the Capitol on Monday evening.

“If we can actually provide and chart out a future that is more leaning into the needs of working people,” she said, “then I think we can chart a path to win.”