WASHINGTON — At a moment of existential turmoil for President Joe Biden, Rep. Alexandria Ocasio-Cortez, D-N.Y., has stepped up as a firm ally of the embattled incumbent, using her platform to speak out against the flurry of Democratic voices who are calling on him to withdraw from the 2024 presidential race.

As former President Donald Trump was wrapping up his lengthy speech accepting the GOP presidential nomination Thursday, AOC — as she’s widely known — took to Instagram Live to speak directly to thousands of followers to make the case against Biden dropping out.

She questioned the viability of replacing Biden atop the ticket at this late stage, warning that some Republicans would challenge that legally and said doing so could lead to “a presidential election being decided by Clarence Thomas and the Supreme Court,” like in 2000.

Ocasio-Cortez emphasized, repeatedly, that she respected the view of ordinary voters who want to see a change atop the ticket and said she wasn’t guaranteeing that Biden would win if he stayed in the race. But she warned that things could get more chaotic for Democrats if Biden were to make the extraordinary move to end his campaign just weeks before the Democratic convention.

“If you 10,000% are super-convinced that the candidate, or president, cannot beat Donald Trump, then do what you think is in your good conscience. But I have not seen an alternative scenario that, I feel, does not set us up for enormous peril,” she said.

In a twist for the left-leaning Ocasio-Cortez, her comments make her among the more forceful pro-Biden voices in the party right now. While over 10% congressional Democrats have called for Biden to withdraw from the race, few have spoken out to criticize those voices and make the affirmative case for him to stay in, with party leadership saying they’ll support any decision he makes.

While backing the president, Ocasio-Cortez and other prominent progressives have, in recent days, persuaded Biden to embrace several of their priorities in a potential second term — including expanding Social Security, capping rent increases, eliminating medical debt from credit reports and slapping term limits on the Supreme Court.

Many progressives, including Ocasio-Cortez and Sen. Bernie Sanders, I-Vt., are primarily driven by policy goals and know they have Biden’s ear. If he steps down, it’s unclear who would replace him and how that relationship would change.

But others are fearful of a Trump presidency if this ticket remains, and there’s no clear consensus about whether Vice President Kamala Harris would be a better or worse prospect, electorally or at governing.

“Right now folks are in existential crisis, emergency mode,” a progressive strategist said of the mood within the movement. “S—’s hitting the fan. … There is this chaos angle on the other side of: If there’s a change in the ticket, then what?”

The strategist said part of the reason progressives like Ocasio-Cortez are backing Biden is the “bird in hand phenomenon” — there’s a “comfort level” with Biden in the White House.

Ocasio-Cortez’s view is not shared throughout the Congressional Progressive Caucus. The day after her livestream, Rep. Mark Pocan, D-Wis., a former co-chair of the CPC, called on Biden to withdraw.

“We must face the reality that widespread public concerns about your age and fitness are jeopardizing what should be a winning campaign,” Pocan said in a joint message to Biden with three other House Democrats. “These perceptions may not be fair, but they have hardened in the aftermath of last month’s debate and are now unlikely to change. We believe the most responsible and patriotic thing you can do in this moment is to step aside as our nominee while continuing to lead our party from the White House.”

During her Instagram Live, Ocasio-Cortez said that much of the effort to push Biden out of the race in the wake of his poor debate performance is coming from “the donor class” and “elites” who would not allow “an easy transition” to Harris becoming the nominee, though she did not opine on Harris — or any other alternative.

“If you think that there is consensus among the people who want Joe Biden to leave that they will support Kamala — Vice President Harris — you would be mistaken,” Ocasio-Cortez said. “I’m in these rooms. I see what they say in conversations. A lot of them are not just interested in removing the president. They are interested in removing the whole ticket.”

She said the effort is being fueled by wealthy donors: “When I’m talking to folks in rooms, I hear, ‘My donor this, my donor that.’ Those are the inputs that I am hearing reflected by my colleagues. It’s not, ‘My voters this…’ it’s like, ‘Big donors are saying this.’”

“I could give two damns about what a bunch of rich people think,” she added.

The progressive strategist also said Ocasio-Cortez, in accusing donors and elites of wanting to eject the whole ticket, may be “pre-butting” the inevitable questions if Biden does quit about whether the nomination should go to Harris or if there should be an open primary.

Her office had no further comment beyond her extensive remarks to followers on the platform. Biden, for his part, has repeatedly and emphatically said he won’t drop out. He said he will return to the campaign trail next week after self-isolating with a Covid diagnosis.

Lisa Lint-Vander Zouwen, a 46-year-old Grand Rapids resident and mom of two school-aged daughters, called herself a “reluctant” Biden supporter. She said she’d like to see him step aside and replaced with a “strong woman” — but not without a competition.

“It would be nice for three to be some sort of process,” she said. “I don’t know what that would look like, but some coming together of the Democrats to discuss who they think would be a strong candidate and why, and not necessarily default to Vice President Harris.”

Ocasio-Cortez also cautioned followers that Biden has unique electoral strengths that other Democrats cannot expect to replicate.

“Joe Biden kind of stomps with older people electorally, which is one of the strongest and most consistent electorates, and it’s actually a hard electorate for Democrats to win. Those are not people that are on Twitter,” she said. “You cannot assume that electorate transfers to any other candidate.”