The story of Buttigieg’s second-choice surge began months earlier, when his campaign decided to go all-in on building an army of highly trained persuaders to deploy on caucus night, after raising a huge $25 million in the spring and spending part of the summer figuring out how to best spend it.

Coaching up volunteer precinct captains is a focus of any competent campaign, and Sanders’ operation had notable success as well, organizing their way to huge wins in the new “satellite caucuses” that could lead to an overall victory for the Vermont senator. But Buttigieg’s team thought the organizers’ role on caucus night would be more important than ever because of a key discovery last year.

Iowa Democrats were so satisfied — or overwhelmed — with their options in the 2020 presidential field that an unusual number of them signing “commit-to-caucus” cards for multiple campaigns. The result: Campaigns had an incomplete picture of how much hard support they had, and more voters were up for grabs. That was reflected in polling, too, with more than a third of Iowans were still undecided just weeks before the caucuses.

“It became clear that voters were signing several commit-to-caucus cards, so that data was not going to be as reliable or useful in a typical caucus,” Brendan McPhillips, Buttigieg’s Iowa state director, told POLITICO. “We wanted exceptionally well-trained people greeting those undecided voters when they walked in on caucus night.”

So “the focus became building up a precinct caucus-night machine,” McPhillips continued. “That was the top priority."

The emphasis on late persuasion in every single precinct dovetailed with other factors that turned Buttigieg’s way in the final days, including former Vice President Joe Biden’s crumbling support and lower-than-expected turnout that benefited better organized campaigns. Buttigieg also poured significant resources into heavy TV advertising and pre-election door-knocking, like his rivals; in order for caucus-night persuasion to work, enough voters had to have information about Buttigieg and be considering him as an option in the first place.

The candidate supplemented those campaign efforts with a go-everywhere travel schedule that included much more attention to rural areas than many of his competitors. It also didn’t hurt that Buttigieg’s mayoral term ended in January, just as his Senate rivals were getting trapped in Washington by President Donald Trump’s impeachment trial, emptying Buttigieg's schedule for an all-out push.

Buttigieg held more than 50 town halls over three weeks, tracked on the wall of his campaign headquarters by an increasingly thick forest of green push-pins marking a map of Iowa with the places the mayor had visited.

"Pete gave something for everybody to like: He’s young. He’s gay. He’s a vet. He’s somewhat moderate-ish."

“He did well in the suburbs, he did well in the rural counties and he did well along the Mississippi River, areas that are blue-collar, manufacturing centers,” said Jeff Link, an Iowa-based strategist who didn’t work for a candidate in the 2020 caucuses. “His unity message struck a chord.”

“Pete gave something for everybody to like: He’s young. He’s gay. He’s a vet. He’s somewhat moderate-ish,” said one Iowa Democratic operative, granted anonymity to discuss the issue candidly. The operative continued: “He could’ve been so malleable that no one went to him at all, but in the end, that non-offensiveness turned into a strength because he could be satisfactory second choice.”

There was a time when it looked like Buttigieg was letting the enthusiasm he had generated slip through his fingers in Iowa, though.

Last April, after breaking through in the national media and the polls, Buttigieg drew 200 people to a mid-afternoon, Tuesday meet-and-greet in Fort Dodge, Iowa, and not a single organizer collected names, phone numbers, or email addresses of attendees — the fuel that powers campaign efforts to find, mobilize and persuade potential supporters on Election Day. Again, later that trip, another 1,600 people gathered on a lawn outside Franklin Middle School in Des Moines. But just two organizers attempted to canvass the crowd, to little effect.

"There were no clipboards, there were no organizers capturing the data of the of the people who were there,” said J.D. Scholten, a congressional candidate challenging Rep. Steve King in western Iowa who introduced Buttigieg in Fort Dodge back in April. “I told his staff after the event, ‘You’re missing out, and you’ve got to fix this,’ and the campaign said, ‘Yeah, we don’t have that figured out yet.”

An Iowa operative for a rival campaign said that looking at Buttigieg then, it felt like “this is a campaign that just doesn’t get it. But they figured it out before long. They figured it out once they got the money.”

After Buttigieg raised $25 million that spring, among the largest fundraising quarters any Democrat had in 2019, the campaign’s senior staff grew to include more experienced operators, like Jess O’Connell, the former CEO of the Democratic National Committee, and Michael Halle, who worked on the Obama and Clinton campaigns. By mid-August, the senior staff met in the campaign’s Des Moines office to “brainstorm what we needed to do to show that we were a campaign that could be taken for real,” McPhillips said.

The next month, the campaign opened 20 field offices in 20 days, growing into one of the biggest field operations in the state.

“Pete certainly exceeded expectations,” said Iowa state Sen. Joe Bolkcom, who endorsed Warren. “Pete obviously started very late, but he put together a top-rate organization in the end.”

Buttigieg’s Iowa strategy also focused on running up the delegate score in rural counties, particularly those that flipped from Barack Obama to Donald Trump in 2016.

The smaller number of voters per precinct meant a handful of personal touches could be decisive, and the Iowa caucuses’ complicated rules meant campaigns could get more state delegates per raw vote there than in the bigger suburban or urban precincts. For Buttigieg, there’s an ironic twist to that strategy: The caucuses' system of awarding state delegates loosely mimics the Electoral College, a system he says he wants to eliminate.

But it worked well. Among the top four candidates, only Buttigieg and Biden performed better in precincts the smaller and more rural they got, while Sanders and Warren did worse, according to a POLITICO analysis of the Iowa results. Even so, Biden missed the viability threshold in most of the smallest quarter of precincts that caucused Monday. Buttigieg, meanwhile, was viable in the vast majority of them, slowly racking up small number of delegates that provided a major chunk of his final winning margin.

“He played the map in a really smart way,” said Lara Henderson, an Iowa-based strategist who worked for Sen. Kirsten Gillibrand’s presidential campaign before Gillibrand dropped out of the race last year. “He dominated in the suburbs and took advantage of rural areas, and I haven’t seen any counties he’s not in the top two or three, and that’s what you’ve got to so. Be viable everywhere, if you can.”