Sen. Bernie Sanders (I-VT) is maintaining his support for Joe Biden even as cracks start to form in the progressive coalition standing with the president.

Sanders, who cemented his status as the leader of the progressive movement by challenging Hillary Clinton and then Biden for the presidential nomination, has since emerged as an establishment ally. He, along with “Squad” Democrats including progressive icon Alexandria Ocasio-Cortez (D-NY), have resisted calls for the president to drop out of the 2024 race following a disastrous debate performance that fueled concerns over his mental fitness.

The support reflects their unorthodox alliance with a man considered a moderating voice in the Democratic Party. As recently as a month ago, they were criticizing him over his handling of the war in Gaza but have used the relationship to steer him toward more populist policies and rhetoric.

“The president can win, and I think he will win,” Sanders told reporters on Wednesday with a caveat: Biden needs to focus on “specific ideas that are going to improve the lives of the working class in this country.”

Sanders has not fully embraced the president as he faces a crisis of confidence within his party. Asked if Biden should remain the Democratic nominee, Sanders merely stated, “The president is the nominee, as I understand it.”

But his defense of Biden, on the campaign trail and cable television, stands in contrast to a small but growing number of progressives looking for a new face atop the Democratic ticket. 

Sen. Peter Welch, his Vermont colleague, became the first Senate Democrat to call on Biden to drop out Thursday, while four members of the Congressional Progressive Caucus have done the same.

The chairwoman of that caucus, Rep. Pramila Jayapal (D-WA), released a statement earlier this week acknowledging the conversations taking place among her membership on the “best path forward to protect our democracy.”

Progressives have been one of the core constituencies standing with Biden in the two weeks since he delivered a sluggish debate performance in which he often lost his train of thought. He also has the support of leaders in the black and Hispanic caucuses.

But Democrats are clamoring for more unscripted moments from the president, who relies heavily on a teleprompter at campaign events and has taken a cautious approach to post-debate interviews.

He will get his next chance to ease concerns at a Thursday press conference on the NATO alliance, but some fear the question of Biden’s age — he would be 86 by the end of a second term — will haunt him for the next four months.

The media portrayal of each public appearance by Biden as a high-stakes moment for his fledgling candidacy suggests the “question of aging capacity simply won’t go away,” Welch told reporters.

“It’s hard to see it. That was a big concern of voters going into the debate and that concern intensified after,” he added.

Sanders, who is 82, has deflected concerns over Biden’s age by chiding those treating the presidential race like a “beauty contest.”

“It is a contest of who stands with the vast majority of the people in this country, the elderly, the children, working class, the poor,” he said on CBS News Sunday. “And that candidate is obviously Joe Biden.”

Meanwhile, Ocasio-Cortez rebuked her fellow Democrats on Thursday for feeding into the sense of panic that party leaders want so desperately to keep behind closed doors.

“The way that our party conducts itself in public contributes just as much to our political challenges as any facts on the ground,” she told reporters.

Sen. Elizabeth Warren (D-MA), another progressive senator who has stumped for Biden, affirmed her support for the president earlier this week, calling him an “excellent president.” She, too, challenged Biden for the presidential nomination in 2020.

For now, the Biden campaign’s biggest concern is vulnerable incumbents whose races will decide control of Congress in November. Polling shows the president falling further behind former President Donald Trump in a spate of swing states, leading to fears he will harm the campaigns of lawmakers running down the ballot.

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But the fact that Democrats in safely blue states are openly alarmed — Biden won Vermont by more than 30 points — suggests the president will have trouble keeping the slow-rolling revolt from ballooning.

His top political advisers will meet with Senate Democrats on Thursday in an off-campus lunch where they are expected to argue Biden is still within the “margin of error” even as they concede he has slipped in the polls.