Ocasio-Cortez’s move came after a months-long courtship that included meetings in Burlington, Vermont late last month between her and Sanders. She was joined by another member of the so-called “Squad,” Rep. Ilhan Omar, who also informed Sanders of her endorsement on a phone call after his heart attack, according to a source familiar with her decision. A third Squad member, Rep. Rashida Tlaib, is expected to announce soon she is backing Sanders as well, though she said Wednesday she hasn't made an endorsement yet.

Ocasio-Cortez’s support is a coup for the Vermont senator and a setback for his liberal rival, Elizabeth Warren. It came at an opportune time for Sanders, whose campaign was thrown into uncertainty after he was hospitalized for a heart attack early this month. Even before that, Sanders had been overtaken by Warren in early-state and national polls.

Sanders' aides and allies did not hide their excitement: Some of them burst into tears and embraced one another after news of the endorsements broke.

“The man who’s really been building the movement for a long time is hospitalized with a heart attack. At his age, no one thinks that’s a good thing for the campaign,” said Waleed Shahid, the communications director for the progressive group Justice Democrats, which formed out of Sanders’ 2016 campaign and recruited Ocasio-Cortez to run for Congress. “To have an endorsement right now is to continue to say this is a campaign that’s important to progressives and people on the left.”

Sanders and Ocasio-Cortez will make their debut together on the campaign trail Saturday in New York City. Their rally is certain to draw comparisons to the large crowd that greeted Warren in the city’s Washington Square Park last month. It probably won’t be their last event: The teams are discussing more rallies across the primary states.

“We certainly hope that she will be campaigning throughout the fall with the senator,” said Sanders senior adviser Jeff Weaver.

Ocasio-Cortez was an organizer on Sanders’ 2016 campaign and several of her aides have come from his team. But she had been complimentary of Warren and had held off on endorsing.

Perhaps sensing an opportunity, Warren had been aggressively cultivating a relationship with Ocasio-Cortez, penning an effusive piece about her for the TIME 100 and partnering with the freshman’s office on several congressional efforts.

Asked about the endorsements on CNN following Tuesday night’s debate, Warren said “[L]ook, I have great respect for all three of those women. I think they are terrific. And here’s what I know for sure, when this primary is over, we are all going to be on the same side.” Her campaign declined to comment further.

Sanders’ aides sensed that Ocasio-Cortez’s endorsement was within reach after she traveled to Burlington in late September to talk with Sanders and his team about her priorities, especially the Green New Deal. It’s not clear who proposed the meetup in Vermont, but Shakir scheduled an hour-plus brunch between Ocasio-Cortez and Sanders. Shakir joined them, as did Jane Sanders and an aide to the congresswoman.

“I remember when they sat and talked to each other, it just felt like people who just know each other and understand each other,” Shakir said. “They have been to some degree within their own caucuses — whether it's the House caucus or the Senate caucus — made to feel that they're outsiders looking in. And I think they find [a] common bond in that: That we are in a struggle where even the establishment of the Democratic Party doesn't always appreciate how we're approaching these issues.”

Omar, meanwhile, told her fellow Squad members that she had decided to endorse Sanders shortly after laying out her criteria for a candidate at the “People’s Presidential Forum” in Iowa last month, according to the source familiar with her decision. She had been thinking about joining Sanders for some time, the person said, and talked with her allies about the importance of not following the polls but instead endorsing a candidate based on the issues.

“The hospitalization raised the stakes a lot, emotionally and politically,” said Alexandra Rojas, the executive director of Justice Democrats. “They are all movement people, they are all organizers at heart, and they were inspired by what he started in 2016,” she said of the members of Congress who endorsed Sanders.

Warren’s foreign policy, which is seen by some progressives as more hawkish than Sanders’, was a factor in Omar’s decision to endorse him over the Massachusetts senator. In a video released Wednesday, Omar said Sanders is “the only candidate that wants to make sure that we end our endless wars.”

Omar is planning to hit the trail for Sanders, and the senator is looking to do a future rally with Tlaib, whose district is in Michigan. Sanders announced Wednesday that he is joining Tlaib for a tour of her district later this month. He pulled off an upset victory in that state in the 2016 primary in part because he won over huge swaths of Muslim voters. Tlaib and Omar are the first Muslim women elected to Congress..

The lawmakers and Sanders are also in talks about doing promotional videos for him. Their support could potentially help Sanders shore up his support among young people, who have long been a key part of his base but which he has been bleeding somewhat to Warren in some polls.

The endorsements come as Sanders has begun drawing sharper contrasts with Warren. He has proposed plans for a wealth tax, student loans cancellation, and climate change that are more far-reaching than hers. And in an interview last week, Sanders said Warren “has said that she is a capitalist through her bones — I'm not.”

Weaver said the Squad members’ endorsements of Sanders will “further cement his leadership of the progressive wing of the Democratic Party.”

“I think it’s time for progressives to come together,” he said, “and defeat the conservative wing of the party and win the nomination and defeat Trump.”

The endorsements and a strong debate performance Tuesday night breathed new life into Sanders’ campaign after weeks of internal anxiety. “You know, to quote one of my favorite rappers LL Cool J, ‘Don’t call it a comeback, I’ve been here for years,’” said Nina Turner, a co-chair of the Sanders campaign.

An exuberant Weaver said to expect Sanders to work as hard as ever. “Imagine Bernie now,” he quipped, “with 100 percent blood flow.”