On a brisk September morning in New Hampshire, Pete Buttigieg leaned against the wall of a newly opened campaign office and contemplated just how far he'd come in his bid to become president. It had been only in January, he told me, that his entire long-shot-campaign operation had consisted of, as he put it, “five people sitting in a room in South Bend” whose number one job was “letting people know we exist.” Now Buttigieg typically had twice that many people in just his traveling entourage—a retinue of aides, videographers, private-security agents, and others trailing in his wake as he crisscrossed the country. His existence was sufficiently well-known that his campaign events now drew crowds in the hundreds and sometimes thousands.

On this morning he was in the quaint town of Conway to open up his 11th campaign office in the first-in-the-nation primary state. Later that day, he'd open the 12th, in the mill town of Berlin. By the end of the month, he would have 20 offices up and running in Iowa, which will hold the first-in-the-nation caucus. Each one was staffed with cadres of young people who'd uprooted their lives and moved to new towns to work as campaign organizers.

Outfitted in “BOOT EDGE EDGE” T-shirts, they pledged honor to what Buttigieg called his Rules of the Road—a list of campaign principles, freshly stenciled on the wall of the Conway campaign office, that ran from traditional corporate-speak (“respect,” “teamwork,” “responsibility”) to millennial aspirations (“joy,” “belonging”). “It kind of started out on a napkin. A proverbial napkin—I think it was actually a Google doc,” Buttigieg explained. “But I wanted to make sure that as this grows, we don't lose the character of the campaign.”

To the 37-year-old candidate, the most meaningful—and in some respects most baffling—sign of that growth was those youthful campaign workers. “I'm not that removed in years from their experience, so I think I'm particularly sympathetic to them,” Buttigieg said. In his white button-up shirt and jeans, he didn't even look that different from some of his troops. “But I'm also humbled by them,” Buttigieg went on. “Maybe I shouldn't be as a candidate at this level, but there's still a part of me that's just amazed that young people are willing to turn their lives upside down and work this hard for this cause.”

That the project of electing Buttigieg president has become a plausible one, much less in some quarters a cause, is the most surprising political development of 2019. It's surprising, of course, because Buttigieg is the not-yet-40-year-old mayor of the fourth-largest city in the country's 17th-largest state—a man who started the race as a virtual unknown.

In the weeks after his New Hampshire visit, as Buttigieg shifted into a more moderate lane and rode a strong debate performance, his potential path to the nomination began to seem increasingly viable, to the point that some in the Democratic establishment were turning away from Joe Biden and toward Buttigieg as the candidate they hoped could defeat their twin bêtes noires—Bernie Sanders and Elizabeth Warren. By mid-November, a Des Moines Register poll found him in first place in Iowa—16 points ahead of where he was just two months ago.

Indeed, Buttigieg has become so recognizable, so fast, that it's almost easy to forget just how unusual his arrival was—or gloss over just how deeply his impact may be felt for years ahead. It's how Mayor Pete has fashioned himself into a serious contender for the White House that has made his campaign so consequential. Embracing his age as a reason for, rather than an obstacle to, his bid, Buttigieg has articulated a generational vision of change that's been particularly welcome in a race that has been dominated by a quartet of septuagenarians. “There is no such thing as an honest politics that revolves around the word again,” Buttigieg said when he formally entered the race in April. “It's not just about winning an election—it's about winning an era.”