(CNN) As the clock ticked toward midnight at a divey pizza joint in Des Moines last month, two of Cory Booker 's top campaign aides didn't know whether it was the beginning of the end, or a new beginning.

The next day, their candidate and 16 others would take the stage at the Polk County Steak Fry, a major event on the Democratic calendar in Iowa for White House hopefuls. But they were about to raise the stakes even further.

Over greasy slices and novelty tiki cocktails, Booker senior adviser Matt Klapper and deputy campaign manager Jenna Lowenstein laid out for Jennifer Palmieri the campaign's audacious gambit: In the morning, they would announce a push to raise $1.7 million in 10 days; and, if they missed their target, Booker would drop out of the race

By Monday, it was clear that going all in had paid off. After hitting $1.7 million Sunday evening, more than one day ahead of their deadline, the campaign surged past $2 million by the end of the quarter Monday night.

It wouldn't be the end of Booker's challenges, financial or otherwise; his polling has stalled in the low single digits, and he has not yet met the polling threshold to qualify for the November debate.

But the fundraising sprint helped lift Booker's campaign to its best quarter of the cycle, his campaign announced Tuesday, with a total haul of $6 million.

"I'm staying in this race," Booker said in a statement Monday morning, "and I'm in it to win."

Palmieri, a veteran of Hillary Clinton's 2016 campaign and the Obama White House, had admittedly been skeptical of the plan.

"I told them I thought it was risky because, I said, I'm not sure that you want to be the one that invites the notion of dropping out into your campaign," Palmieri, who isn't connected to a particular campaign this cycle, recounted. But Booker's team had already considered this and other possible pitfalls and concluded they had no other choice.

"They had much more serious money problems than people knew."

Booker's campaign says it was not on the brink of insolvency. On their path prior to their 10-day bet, the campaign insisted, they could have sustained until the Iowa caucuses. But their fundraising had taken a significant hit during the crucial third quarter before the primary season, when they needed to be preparing to scale up — not retrenching. That is, if they wanted a shot to win.

This is the story of Booker's surprising gamble to save his presidential campaign, based on interviews with half a dozen aides, as well as outside supporters and other Democrats. Those inside the campaign spoke with CNN on condition of anonymity to freely discuss internal strategy and deliberations.

"We forced the crisis," one senior campaign aide explained, "because the crisis in its truest form was going to come too late."

An idea is born

Presidential candidate and U.S. Sen. Cory Booker attends the Democratic Polk County Steak Fry on September 21, 2019 in Des Moines, Iowa. Seventeen presidential candidates attended the Polk County Steak Fry.

The campaign started to see red flags in September, when an anticipated fundraising surge never materialized. After the third Democratic debate in Houston, "the trajectory of the budget changed very fast," according to one senior aide.

At a sushi lunch the following week, Lowenstein brainstormed how to course correct with Emily Norman, the campaign's chief innovation officer; and two members of the campaign's digital team, Alex Witt and Catherine Gabel.

It was Norman who suggested going public with the campaign's fundraising shortfall.

"Let's be honest with people," she said, reasoning that voters liked Booker and would want him as an option in the early primary states, even if they weren't ready to commit to him yet. Norman guessed that many Democrats assumed Booker had enough money to remain competitive, and would lend their support to the campaign if they understood the starker reality.

It sounded crazy — but then, they shrugged, wasn't this primary already sort of weird? Toward the end of a small senior staff meeting that week with campaign manager Addisu Demissie and Klapper, Lowenstein threw out the idea.

They each argued for it and argued against it; then they marinated on it. Ultimately, when they brought a menu of options to Booker, they recommended the highly unorthodox scheme.

"All of us were at a point where we were just open and looking for things to shake up what has been a very stagnant race," one senior aide said. They believed, and Booker agreed, that this course of "radical transparency" would reflect the values of the campaign — and, maybe, it could work.

Once Booker greenlit the plan, his campaign had roughly 48 hours to orchestrate a rollout and plot the 10-day push to come. For their fundraising target, they settled on a number that was ambitious but, under near-perfect conditions, attainable: $1.7 million, more money than Booker had raised during any 10-day period since he entered the race.

Booker "was completely sober about the challenge, and totally ready to run at it," one senior aide said. But as staff began to learn of the campaign's financial state and the challenge ahead, "there was a mix of shock and a little bit of, 'shit,'" another aide recalled.

"We knew we needed to do it," another senior aide said. "We didn't know if we could do it."

On September 20, the evening before the Steak Fry, as Booker was campaigning in Cedar Rapids, Iowa, they began to inform donors and supporters of their plans. Outside of an LGBTQ forum, Klapper paced back and forth furiously, his ear to his phone.

Cedar Rapids Councilman Dale Todd, who has endorsed Booker, saw the candidate and his team that evening and learned the news firsthand. Booker was ebullient as ever, Todd recalled. For his part, Todd said he never questioned their strategy nor thought of jumping ship.

"I would rather have a great candidate with no money than a lousy candidate with a lot of money," Todd said. "We can beat the money hands down."

As Booker and his team drove to Des Moines that night, with Klapper, Lowenstein and Iowa state director Mike Frosolone in the car, Booker called to share the plan with his Iowa staff, who had spent long days preparing for the Steak Fry and now would be executing under very different circumstances.

It wasn't clear how they would respond.

"You're telling people who have poured their lives into something that there is a chance that it could end," one senior aide said. "But it was laced with a sense of purpose and optimism, that it was in our hands."

The rest of Booker's staff learned about the pivotal 10 days ahead when NBC News broke the story the following morning, and Demissie emailed his team to confirm it. Booker joined an all-staff call to rally his troops, saying he could "see victory."

"He talked about envisioning caucus day in Iowa and New Hampshire primary day," a senior aide said, "and this was just part of the story."

Rallying support

Democratic presidential candidate Sen. Cory Booker flips veggie burgers at the Polk County Democrats Steak Fry, in Des Moines, Iowa, Saturday, September 21, 2019.

Rob Sand, the Iowa state auditor, was taking a break from hunting elk in New Mexico when he saw the news breaking on Twitter.

"And instantly I just thought, that's terrible," he told CNN this week.

Immediately, Sand filmed a short selfie video in which he praised Booker's "unique voice" in the primary, saying he stood out as "the strongest uniter." Sand wasn't endorsing Booker, he noted, still wearing his hunting camo, "but I do know that I want him in the race."

Sand was one of the first elected officials and influential Democrats to speak out in support of Booker, but he wouldn't be the last. That first day and in the days to come, Georgia Democrat Stacey Abrams, New York Sen. Kirsten Gillibrand, Mayor Muriel Bowser of Washington, DC, and others would encourage their supporters to donate to Booker, though none went so far as to endorse him.

The overwhelming response befuddled and frustrated some of Booker's rivals.

"When the only tactic to bring in significant fundraising is a threat to drop out, that's cause for alarm, not celebration," said one aide to another Democratic presidential campaign. "Hey, I gotta give them credit for taking a big gamble that paid off. I respect the hustle. But the bigger question is: why did a lot of establishment Democrats unify around him to help him cross that bridge?"

The rival aide added: "That's $1.7 million sucked out of the pool and poured into a campaign that, by their own admission, was going nowhere. At a time when most people want to winnow the field, it just struck me as odd that there was a broad effort to prop up a campaign that said they were failing."

Photos: Former presidential candidate Cory Booker Photos: Former presidential candidate Cory Booker US Sen. Cory Booker greets the audience at a Conference of Mayors meeting in January 2019. Hide Caption 1 of 41 Photos: Former presidential candidate Cory Booker Booker's parents, Cary and Carolyn, were among the earliest black executives at IBM. The family grew up in the affluent community of Harrington Park, New Jersey. Cory is third from left. His younger brother, Cary, is with his dad at left. Hide Caption 2 of 41 Photos: Former presidential candidate Cory Booker Booker played football at Stanford University. He also served as student body president and ran a crisis hotline for students. After getting his master's degree, he would go on to attend Oxford University as a Rhodes Scholar. He graduated from Yale Law School in 1997. Hide Caption 3 of 41 Photos: Former presidential candidate Cory Booker Booker, second from left, poses with his parents and his brother after he was elected to the Municipal Council of Newark in 1998. It was his first public office. Hide Caption 4 of 41 Photos: Former presidential candidate Cory Booker Booker concedes defeat after losing the 2002 mayoral race to incumbent Sharpe James. But he would be back four years later. Hide Caption 5 of 41 Photos: Former presidential candidate Cory Booker Booker celebrates in May 2006 after he was elected as Newark's mayor. He defeated Deputy Mayor Ronald Rice after incumbent Sharpe James decided to focus on the state Senate. Hide Caption 6 of 41 Photos: Former presidential candidate Cory Booker Booker takes the oath of office in July 2006. Next to him, holding the Bible, is his mother, Carolyn. Also holding the Bible in the foreground is Booker's grandmother, Adeline Jordan. Hide Caption 7 of 41 Photos: Former presidential candidate Cory Booker Booker walks on the newly refurbished City Hall dome in Newark in November 2006. Hide Caption 8 of 41 Photos: Former presidential candidate Cory Booker From left, Booker, Lt. Gov. candidate Loretta Weinberg, US President Barack Obama and New Jersey Gov. Jon Corzine wave at a gubernatorial campaign rally in November 2009. Hide Caption 9 of 41 Photos: Former presidential candidate Cory Booker Booker helps cut the ribbon at the opening of affordable housing in Newark that was funded through Jon Bon Jovi's JBJ Soul Foundation in December 2009. Hide Caption 10 of 41 Photos: Former presidential candidate Cory Booker Booker stands behind Facebook CEO Mark Zuckerberg, who donated $100 million to help improve public schools in Newark. His donation was the first grant handed out by his new foundation, Startup: Education. The foundation is focused on bettering education in the United States. Hide Caption 11 of 41 Photos: Former presidential candidate Cory Booker Booker shovels snow to help dig out people's vehicles in Newark in January 2011. While serving as mayor, Booker developed a reputation for engaging in personal acts of heroism such as rescuing a neighbor from a house fire and chasing down a suspected bank robber. Using social media to connect with constituents, he shoveled snowbound driveways by request and invited nearby city residents to his home when Hurricane Sandy caused widespread power outages. Hide Caption 12 of 41 Photos: Former presidential candidate Cory Booker Booker leaps from the wheel cover of a mobile billboard after taking photos on it in February 2011. The truck was driven across the nation to draw attention to US gun laws. Hide Caption 13 of 41 Photos: Former presidential candidate Cory Booker Booker plays a game of one-on-one with pro basketball player Cappie Pondexter in May 2011. Hide Caption 14 of 41 Photos: Former presidential candidate Cory Booker Booker speaks at the Democratic National Convention in September 2012. Hide Caption 15 of 41 Photos: Former presidential candidate Cory Booker Women pose next to Booker's campaign bus during a rally in Newark in August 2013. Booker was running for the US Senate seat that was vacated when five-term incumbent Frank Lautenberg died at the age of 89. Hide Caption 16 of 41 Photos: Former presidential candidate Cory Booker Booker addresses supporters after winning the Democratic primary in August 2013. He went on to defeat Republican Steve Lonegan in October. Hide Caption 17 of 41 Photos: Former presidential candidate Cory Booker Booker takes the oath of office from Vice President Joe Biden during a ceremonial swearing-in at the US Capitol. Hide Caption 18 of 41 Photos: Former presidential candidate Cory Booker Booker confers with US Sen. Kirsten Gillibrand during a Senate subcommittee hearing in November 2013. The hearing, about Hurricane Sandy recovery efforts, was Booker's first since being sworn in. Hide Caption 19 of 41 Photos: Former presidential candidate Cory Booker Booker addresses a gathering of students and parents at his childhood school in Harrington Park, New Jersey, in November 2014. He had just been re-elected a day earlier. Hide Caption 20 of 41 Photos: Former presidential candidate Cory Booker Booker testifies before the Senate Judiciary Committee's Constitution, Civil Rights and Human Rights Subcommittee in December 2014. Hide Caption 21 of 41 Photos: Former presidential candidate Cory Booker Vice President Joe Biden administers the Senate oath to Booker in January 2015. Holding the Bible is Booker's niece, Zelah, and his sister-in-law, Lucille. Hide Caption 22 of 41 Photos: Former presidential candidate Cory Booker Booker talks with US Sen. Chuck Schumer after a news conference about Iran in October 2015. Hide Caption 23 of 41 Photos: Former presidential candidate Cory Booker Booker meets with eighth-graders during their end-of-year trip to Washington in May 2016. Hide Caption 24 of 41 Photos: Former presidential candidate Cory Booker Booker campaigns with Democratic presidential candidate Hillary Clinton at a cafe in Newark in June 2016. Hide Caption 25 of 41 Photos: Former presidential candidate Cory Booker During a news conference in June 2016, Booker embraces the Rev. Sharon Risher, a clinical trauma chaplain who lost her mother and two cousins in a church shooting in Charleston, South Carolina. Democratic senators were calling for gun-control legislation after a mass shooting at an Orlando nightclub. Hide Caption 26 of 41 Photos: Former presidential candidate Cory Booker Booker speaks at the Democratic National Convention in July 2016. Hide Caption 27 of 41 Photos: Former presidential candidate Cory Booker Booker speaks to members of the media following a confirmation hearing for US Sen. Jeff Sessions, a Republican from Alabama who was nominated to be attorney general. Booker broke with tradition and became the first sitting senator to testify against a fellow senator's nomination for a Cabinet post. Hide Caption 28 of 41 Photos: Former presidential candidate Cory Booker Booker looks on as Scott Pruitt, Oklahoma's attorney general and Donald Trump's pick to run the Environmental Protection Agency, testifies at his confirmation hearing in January 2017. Hide Caption 29 of 41 Photos: Former presidential candidate Cory Booker Booker and US Sen. Elizabeth Warren talk before the start of a July 2017 news conference that introduced the Dignity for Incarcerated Women Act. Hide Caption 30 of 41 Photos: Former presidential candidate Cory Booker Booker boards an elevator at the Capitol in January 2018. Hide Caption 31 of 41 Photos: Former presidential candidate Cory Booker Booker questions Judge Brett Kavanaugh, President Trump's nominee for the US Supreme Court, during Kavanaugh's confirmation hearing in September 2018. Hide Caption 32 of 41 Photos: Former presidential candidate Cory Booker Booker poses for a photo with a group of visitors at the Hart Senate Office Building in Washington in January 2019. Hide Caption 33 of 41 Photos: Former presidential candidate Cory Booker Booker joins actors Taylor Trensch and Rosario Dawson backstage at the hit Broadway musical "Dear Evan Hansen" in January 2019. Dawson confirmed in March that she and Booker were dating. Hide Caption 34 of 41 Photos: Former presidential candidate Cory Booker Booker walks with NAACP leaders during a Martin Luther King Jr. Day march in Columbia, South Carolina, in January 2019. Hide Caption 35 of 41 Photos: Former presidential candidate Cory Booker After announcing that he would be running for president, Booker speaks to the press outside his home in Newark in February 2019. Hide Caption 36 of 41 Photos: Former presidential candidate Cory Booker Booker speaks during a campaign event in Des Moines, Iowa, in February 2019. Hide Caption 37 of 41 Photos: Former presidential candidate Cory Booker Someone takes a photo of Booker during a campaign stop in Claremont, New Hampshire, in March 2019. Hide Caption 38 of 41 Photos: Former presidential candidate Cory Booker Booker looks to be called on during the CNN Democratic debates in July 2019. Hide Caption 39 of 41 Photos: Former presidential candidate Cory Booker Booker explores the Iowa State Fair in August 2019. Hide Caption 40 of 41 Photos: Former presidential candidate Cory Booker Booker is seen after a Democratic debate in Westerville, Ohio, in October 2019. Hide Caption 41 of 41

But where some people saw a failing campaign, others saw one that simply hadn't taken off yet.

The flood of support for Booker from Democrats was "a reaffirmation of what the polls show," said Sand, "which is, he might not be polling as everyone as people's number one choice, but he's definitely someone that a lot of people consider and a lot of people like as a candidate."

"He obviously would be on my shortlist for someone I'd be interested in endorsing," Sand added.

Booker's team had been apprehensive about how their announcement would be received. Would people assume the campaign was dead, rather than rally to save it? As the first day unfolded, however, it became clear that Democrats were answering their call.

When a senior Booker aide saw the personal donation and appeal from Gillibrand, a former 2020 rival, "that was a moment when I was like, oh, people are gonna show up for this."

Booker's network was not only holding together, but energized. The mood "was positive and action-oriented" on a call that afternoon with key donors and supporters, led by Demissie, Klapper and national finance director Lauren Dikis.

"It felt much more like a team huddle," said a source who listened to the call, "like, let's go out and here's the play."

Back at the Steak Fry, it seemed like a relatively normal day on the campaign trail. Booker had planned to mention the fundraising goal in his remarks; but, surprising no one on his team, he got so whipped up in the moment that he skipped right over it.

The message got out anyway. By the end of the first day, Booker's team had posted their best grassroots fundraising haul of the campaign. In 24 hours, they would raise more than $300,000. And the senior team began to think that their impossible mission might be possible, after all.

Lowenstein would fly back from Iowa with $4,000-worth of contributions in her purse. In Newark, Demissie added September 21 to his list of memorable days in more than a decade of working on presidential campaigns. But their work was still far from over.

"We just put a boat in the water and it didn't sink," Booker told Demissie when they spoke that evening. "Now we have to row it to the other side."

Do-or-die

Democratic presidential candidate and U.S. Sen. Cory Booker takes a selfie with a woman during a campaign trail block party on September 29, 2019 in Columbia, South Carolina.

As Booker's team settled into a rhythm, senior aides were gratified to see the campaign's staff rallying around their shared goal. But they were a little uncomfortable with the tattoos.

It had all started after the Steak Fry, when one Iowa organizer asked Booker to write the campaign's motto, "we rise," so that she could have it tattooed on her arm in his handwriting.

Suddenly, more than a dozen Iowa organizers were pledging to ink "we rise" if they hit their fundraising goals. One set his sights on a "baby bonds" tattoo, after Booker's signature policy proposal to shrink the racial wealth gap. Before long, Frosolone, the state director, had also committed to a "we rise" tattoo if his team could bring in $30,000 toward the campaign's goal.

"To be clear, we did not encourage this," one aide said. "This is as grassroots as it gets."

After the initial burst of adrenaline from Booker's do-or-die moment, there was no guarantee that his team would be able to sustain the momentum they needed to reach $1.7 million. But no one seemed to think they were living through the final days of the campaign.

Campaign aides continued to operate as though they would meet their fundraising goal. Events remained on the schedule for after September 30, and plans were already underway to begin scaling up in Iowa and elsewhere.

Meanwhile, Booker did not withdraw from the campaign trail to focus solely on fundraising, instead choosing to keep up a full schedule of travel and events. During the 10-day push, he would hit all three early primary states: Iowa, New Hampshire and South Carolina.

During a stop Thursday at Politics and Eggs in New Hampshire, a must-do stop for candidates, Booker received an enthusiastic response. "Welcome to the Cory Booker rally," Jim Brett, president of the New England council, joked after the crowd gave Booker a standing ovation — an unusual show of support at what is normally a staid event. Afterward, Booker's New Hampshire adviser Jim Demers collected checks for $500 and $1,000 from two people he had never met.

"Nobody ever goes to that event and leaves with campaign contributions," Demers said.

Later that evening, Booker was running through the halls of CNN in New York, ducking behind corners to outrun his campaign aide who was staffing him for an interview with Don Lemon. In the car afterward, the candidate was cracking jokes. And when Booker finally arrived home around 11:30 p.m., he was "still so f*****g cheery and so upbeat," an aide recalled.

If this was a dire chapter in the story of Booker's campaign, it sure didn't look like it.

To keep staff motivated throughout the week, senior aides organized calls each night to field questions and give updates on progress. In the final stretch, the calls also featured surprise pep talks from Booker's girlfriend Rosario Dawson, New Jersey Gov. Phil Murphy and Democratic campaign veteran Marlon Marshall.

When staff logged on Sunday afternoon for their final call before their 10-day deadline, Hillary Clinton's voice came through their AirPods and speakers.

According to a source on the call, Clinton recalled her experiences working on presidential campaigns, including for Jimmy Carter. She expressed her gratitude for Booker's help in 2016, when he was an active surrogate for her presidential campaign. And she cheered on his staff in their own hour of need.

"The best way you can push through this and the challenges ahead is by sticking together," Clinton said.

Next steps

Democratic presidential candidate and Sen. Cory Booker addresses a crowd during a campaign trail block party on September 29, 2019 in Columbia, South Carolina.

By Monday, Lowenstein's fateful sushi lunch had already become the stuff of legend within the Booker campaign.

"The story will one day be told: at a lunch, a number of the great leaders, great women on our campaign, thought up this incredible idea to just open up the curtain and show people behind the scenes of what we needed to thrive and survive," Booker said during a call Monday evening with his staff.

The campaign had just shot past the $2 million mark, five hours before the end of the third quarter, and Booker praised his team's "grit" over the past 10 days. But he also acknowledged the challenges ahead, likening his team to Washington's army in the Revolutionary War, "outgunned and outmatched" by rivals with more money.

"This is going to be a hard quarter," Booker said. "It's also going to be a defining quarter."

Booker's dramatic, desperate fundraising gambit worked this time. But whether his campaign can sustain the fundraising pace it will need to grow is an open question — and the money he raised this week is no panacea, his campaign says.

"To be clear, $1.7 million doesn't get us to where we need to be," one senior aide said. "It just puts us back on a track, and now we'll need to stay on that track."

Among the field of Democratic presidential hopefuls, Booker has never been a standout fundraiser. In the second quarter this year, he raised just $4.5 million — a fraction of the hauls posted by frontrunners Massachusetts Sen. Elizabeth Warren and former Vice President Joe Biden. Booker's team believes there are four campaigns in the top tier of fundraising -- and they are not one of them.

To continue growing, Booker's team has set a $3 million fundraising goal for October. And they hope to begin to address a core issue that has hobbled their fundraising to date: Prior to running for president, Booker did not cultivate a list of grassroots donors, as many other candidates did.

With the fresh infusion of cash, Booker's campaign is now planning a six-figure investment in its email list, Demissie said Tuesday.

Another factor is outside of Booker's control, however.

"Why does Cory Booker have money problems?" Palmieri said. "Because of the debate rules."

Booker, like other second- and third-tier candidates, has needed to expend considerable resources to meet the Democratic National Committee's donor thresholds for the debates.

"If we had one hundred dollars to spend and we wanted to spend ten of it on persuasion, but we weren't that arbitrary donor threshold yet, we had to spend it on the donor," one senior campaign aide said.

The DNC recently announced that candidates would need 165,000 unique donors to qualify for the November debate. Booker's campaign only crossed that threshold this past week, during their fundraising push. And it's possible that that number will go up again.

It's only one of the challenges Booker will need to meet in the coming weeks, as he looks to build support for his underdog campaign. As Booker might say, keeping his campaign alive was just the floor, not the ceiling.

"We'll run through this brick wall, and then Lord knows how many brick walls are going to be on the other side," another senior aide said. "But that, my friend, is a presidential campaign."