WASHINGTON (AP) — At Mike Bloomberg’s midtown Manhattan campaign headquarters, a team of pollsters and analysts churned out multiple tranches of data each day on the state of the Democratic race. The sophisticated data operation was supposed to be the candidate’s not-so-secret weapon, giving Bloomberg an almost real-time look at voters’ preferences in key states and allowing the campaign to rapidly move around its vast resources.

But after Joe Biden’s commanding victory in the South Carolina primary, the numbers moved too fast for Bloomberg’s money to catch up. Voters were rapidly flocking to the former vice president — so quickly that poll results were outdated almost as fast as they landed in the Bloomberg team’s inboxes.

“Even polls that were 24 hours old, 12 hours old were out of date,” said Kevin Sheekey, Bloomberg’s campaign manager.

Just three days after Biden’s South Carolina victory, 10 more states confirmed what Bloomberg and other candidates were seeing: a stunning consolidation of support around Biden by a diverse swath of the Democratic electorate. Though Biden lost California, the night’s biggest prize, to Bernie Sanders, he closed the gap there significantly, allowing him to emerge from Super Tuesday with a lead in the all-important delegate count.

The 72 hours between the South Carolina primary and Super Tuesday pulled Biden back from the brink of elimination and propelled him to the front of the race for the Democratic nomination. His resurgence is one of the most remarkable turnabouts in modern American politics, and sets up a head-to-head competition with Sanders over who is best to take on President Donald Trump in November.

Biden’s comeback was aided by rivals who stepped aside and urged their supporters to back him; by deep connections, particularly with black voters, built up over four decades in politics that helped him overcome significant gaps in his campaign operations in key states; and a growing fear among more moderate Democrats that Biden was the party’s last best hope to stop Sanders, a Vermont senator and self-described democratic socialist, from clinching the nomination.

This account of those three crucial days is based on interviews with a dozen campaign operatives and political allies of the candidates, some of whom insisted on anonymity in order to discuss internal deliberations.

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The morning after Biden’s thunderous, 30-point victory in South Carolina, the Democratic presidential field descended on Selma, Alabama, to commemorate the bridge crossing where civil rights marchers were attacked in 1965.

One had already made a private decision to drop out of the race, and another was weighing whether to do the same.

Pete Buttigieg had spent Saturday night huddled in his hotel room at a Hampton Inn in Americus, Georgia, on a conference call with top aides. One by one, Buttigieg’s aides gave their assessment: The road ahead was bleak.

It’s not where Buttigieg expected to find himself after effectively tying Sanders in Iowa and finishing a close second in New Hampshire. But he didn’t get the burst of momentum out of those states that his campaign had hoped. And while his advisers had expected Biden to win in South Carolina, the margin of victory was surprising.

On the late-night conference call, Buttigieg’s advisers struggled to outline how he would emerge from Super Tuesday in solid position in the delegate count.

Buttigieg agreed with his team’s assessment: It was time to get out.

Senior campaign advisers hurriedly made plans for a concession speech back in Indiana, while Buttigieg dutifully pressed on through his schedule of events on Sunday, including the march in Selma. Between events, he called supporters to let them know his campaign was ending.

Chris Cabaldon, the mayor of West Sacramento, California, was among those who received a call. The candidate seemed a little “shaken,” Cabaldon said, but maintained he was comfortable with his decision.

“I think it was pretty clear he felt not just at peace, but he had a new mission,” Cabaldon said.

Buttigieg also tried to reach Biden, but his team initially had the wrong telephone number. When the two men finally spoke, Buttigieg told the former vice president he was weighing an endorsement, but didn’t make a firm commitment.

Guiding Buttigieg’s decision was a conversation he had earlier Sunday night with Barack Obama. The former president, who has stayed stridently neutral throughout the primary, had long been a fan of Buttigieg, identifying him as one of the Democratic Party’s next generation of leaders.

Obama congratulated Buttigieg on his campaign and counseled him on a possible endorsement, according to a person with knowledge of the call. Obama didn’t push Buttigieg to endorse a specific candidate, but they talked through factors to consider.

By Monday morning, Buttigieg was ready to back Biden. His campaign quietly coordinated with Biden’s campaign, which sent a private plane to South Bend to ferry Buttigieg to Dallas for an endorsement event.

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Sen. Amy Klobuchar was also among the candidates who gathered in Selma. After a surprise third-place finish in New Hampshire and a sudden infusion of cash, her campaign was struggling to keep pace with the campaign’s intense primary calendar.

Klobuchar had spent Sunday morning talking with her own advisers about the path forward. The senator’s home state of Minnesota was among those voting on Super Tuesday, and the campaign’s internal polling showed Klobuchar ahead.

The way Klobuchar saw it, she had two choices: stay in to win Minnesota and relish in the glow of a home state victory, or drop out and help Biden win the state.

Klobuchar reached her decision in Selma, as she sat inside Brown Chapel A.M.E. Church.

“I was in that church in Selma that morning and I was thinking what is better here? What is better for our country?” she said on NBC’s “Today Show." Klobuchar privately concluded she needed to step aside.

Still, she hoped for one last rally in her home state before she announced her decision. It wasn’t to be.

Protesters interrupted Klobuchar’s campaign event at a suburban Minneapolis high school, calling on her to drop out over her handling of a 2002 murder case that sent a black 17-year-old to prison for life while she was a county prosecutor. The rally was abruptly canceled.

Klobuchar got back on the campaign’s charter plane and headed to Utah, where she had a morning event scheduled in Salt Lake City. But she left her aides with instructions: Because time was running out before Super Tuesday, she wanted to hold one event to both announce the end of her campaign and appear with Biden to declare her support for the former vice president.

Campaign manager Justin Buoen and two other campaign aides started Googling where Biden would be on Monday. He had events in Texas, and a nighttime rally in Dallas seemed the most feasible.

Beyond logistics, there was an added bonus to picking the Dallas event. A joint Biden-Klobuchar rally was all but certain to be carried live on cable television.

And it was scheduled for the same time Sanders would be holding a rally in Minnesota.

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For Biden, the three days between South Carolina and Super Tuesday were dizzying.

The campaign had been running on fumes through the opening months of the year. Disappointing finishes in the opening contests scared off donors, and the campaign’s coffers were running perilously low.

But Biden appeared more at home in South Carolina, where his family had vacationed for years and where he had deep ties to state officials and voters. Ahead of the primary, he’d secured the endorsement of Rep. James Clyburn, the highest-ranking African American in Congress, whose backing for Biden had come with a dose of tough love about the ways the campaign needed to improve if Biden had any hope of securing the nomination.

Heading into the Saturday primary, Biden’s campaign was hoping to pull out a win with a margin of victory in the double digits. Biden went on to carry the state by 30 points.

“This is the night Bernie Sanders began to unravel,” Dick Harpootlian, a South Carolina state senator and longtime Biden backer, said at the victory party that night.

At campaign headquarters in Philadelphia, phones began to ring. Establishment Democrats who had held off endorsing and donors who had been sitting on the sidelines were suddenly expressing interest.

One of the centrist Democrats who had backed Biden in the lead-up to South Carolina was Virginia Sen. Tim Kaine, whose state was among those voting on Super Tuesday.

When Kaine first announced his endorsement and appeared with Biden, he sensed that many voters in Virginia were still undecided. But the morning after Biden’s South Carolina win, Kaine said the shift in his state was palpable.

“I had people just coming up to me saying, ‘Hey, I saw that, I’m really glad you did that,’” Kaine said. “People were deciding late, and they were looking for how to figure this out.”

On Super Tuesday, Biden’s margin of victory in Virginia was about as large as it was in South Carolina. His campaign had just one office in the state and had spent less than $200,000 on television advertising compared with $12 million for Bloomberg.

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By the next morning, Bloomberg, too, would be out of the race.

He’d plunged more than a half-billion dollars into his primary campaign, but failed to win a single state.

Bloomberg’s path to the nomination was always contingent on a Biden collapse, and for weeks, the polling the data-driven billionaire consumed backed up that bet.

But Bloomberg’s own favorable ratings took a serious tumble in the campaign’s internal polling after a poor debate performance in February in which Sen. Elizabeth Warren and others berated him for the stop-and-frisk policy he oversaw as mayor of New York and his company’s non-disclosure agreements with dozens of women.

After South Carolina, the campaign’s polling showed the race was rapidly shifting away from Bloomberg. With no financial restrictions, and significant resources already spent, the campaign decided to press forward to Super Tuesday with a long-shot hope of overperforming.

By night’s end, Bloomberg wasn’t close to contention for any of the 14 states. Biden won in Minnesota, in Texas, in Massachusetts — all states where he had a scant campaign operation and little advertising on the air.

The former mayor arrived at his midtown campaign headquarters by about 8 a.m. Wednesday for one last look at the data. He concluded that he, too, was getting out and endorsing Biden.

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AP writers Bill Barrow in Atlanta and Kathleen Ronayne in Sacramento, California, contributed to this report.