BOSTON — The morning after her upset political victory, Ayanna Pressley ascended a stage in Dorchester a few blocks from the John F. Kennedy Presidential Library, greeting activists who had gathered to unify the party and to see a trailblazer — black, female, Bostonian — now poised to assume the old J.F.K. congressional seat.
Outside, around the corner, was Joe Moakley Park, named for the consummate South Boston Irish Democrat who had won 15 terms to Congress. A mile away stood Boston College High School, the proud Jesuit Catholic hub with more than 150 years of history and, lately, flagging application numbers.
“This is a tribal and parochial place,” Ms. Pressley, 44, said Wednesday, surrounded by Boston political leaders old and new as she ruminated on the hurdles that others said would prevent her from winning. . “This hasn’t always been my home.”
It is now.
With her 17-point win over the 10-term Democratic incumbent, Michael Capuano — long a liberal in good standing, undone anyway by his opponent’s message of activist urgency and generational change — Ms. Pressley has done more than make clear that progressive outsiders are here to stay, from Florida (Andrew Gillum) to New York (Alexandria Ocasio-Cortez) to New England.
Here in Boston, Tuesday’s result has registered as something deeper, not only an earthquake disrupting the established political order but a jolt to the very identity of a historic American city, one that likes to call itself “the Athens of America” but is perpetually reckoning with its own reputation for provincialism, particularly on matters of race.
Residents had long understood that the winds were shifting, that the city of “Honey Fitz” and Tip O’Neill and the Bulger brothers had evolved into something new. Technology and finance jobs have flooded in, enticing students from the area’s welter of colleges to stick around after graduation. African-Americans and other racial minorities, galvanized by Ms. Pressley’s message that “change can’t wait,” have made plain that they intend to demand more than a left-leaning voting record in this moment of insurgent fervor.
And places like Somerville, once a solid blue collar suburb where Mr. Capuano had served as mayor, have increasingly gentrified, filling with white progressives with little affinity for the old machine and a strong desire to project maximum resistance to the Trump presidency.
“Living under Donald Trump is exhausting,” said Horace Small, a longtime activist in Boston who is executive director of the Union of Minority Neighborhoods. “It ain’t black and brown people who are the only ones who are exhausted. So are a lot of white people.”
Of course, the first step was supplying voters with a different kind of choice.
Lawrence DiCara, a former City Council president and unofficial Boston historian, recalled the elections of 1960 when Bostonians “could vote an all-Irish ticket,” with J.F.K. at the top and other Irish Catholic men among the candidates for all the other offices.
“Look at all of our mayors over the years,” Mr. Small said. “Look at all the names.”
Walsh. Menino. Flynn. And those are only the most recent.
One of them, Ray Flynn, who later became President Bill Clinton’s ambassador to the Vatican, said the outcome on Tuesday was a welcome signal of a new power structure in the city, even as it followed a familiar arc.
“It’s like the old days,” Mr. Flynn said. “The Irish came into political power. And then the Italians. And then the Polish. And now you’re seeing the immigrant population and the minorities, they’re starting to get some real political strength in Boston. That’s a good thing. That means that they really feel empowered. They feel like they’re part of Boston.”
Taking stock of the fallout on Wednesday, local Democrats vacillated between shock and exuberance. (There was also a bit of justifiable fatigue. After saying she had spent much of the last several months double-fisting coffee and energy drinks, Ms. Pressley canceled an afternoon event, with her campaign citing “some symptoms of dehydration and exhaustion.”)
The gathering in Dorchester, held at Senator Elizabeth Warren’s Boston headquarters, was billed as a “unity event,” and attended by fellow Democrats who may or may not have supported Ms. Pressley’s bid initially. Mayor Martin J. Walsh, who had backed Mr. Capuano, said that Ms. Pressley’s campaign had left people “inspired to make history.”
Maura Healey, the state’s popular attorney general, who had worked on behalf of Ms. Pressley, remarked upon the number of first-time candidates across the ballot on Tuesday. “And you know what?” she said. “A whole bunch of them won. That’s what democracy looks like.”
In what was seen as a victory of sorts for Ms. Pressley during the campaign, both United States senators from Massachusetts — Ms. Warren and Ed Markey — had remained neutral in the race.
In an interview on Wednesday, Mr. Markey seemed to caution against drawing any larger conclusions about state or national politics.
“It’s constructed as a majority-minority district and there were two very good candidates, and ultimately I think the election reflected that those changes had taken place,” he said at the Capitol in Washington, adding: “I don’t think people are reporting a lot of other changes in the statewide races yesterday or in other congressional districts. I’d be hard pressed to predict what will happen in eight more weeks much less two years from now.”
But if nothing else, Ms. Pressley’s upset made clear that enthusiasm matters.
Normally, about 60,000 people might turn out in a Democratic primary in this district, according to John Walsh, a former chairman of the state Democratic Party, who supported Ms. Pressley.
This time, 102,000 voters showed up. Ms. Pressley won nearly 60,000 of them. “If this had been an ordinary primary,” in turns of turnout, Mr. Walsh said, “Michael had the votes to win.”
The Pressley campaign attracted those extra votes through a combination of movement-building, social media and old-fashioned get-out-the-vote methods like sound trucks blaring through neighborhoods on Primary Day.
The campaign did not have the money or the inclination to air traditional broadcast television ads, which would not have been able to successfully target people in the district. Instead, it ran one Spanish-speaking ad on Telemundo and used other local ethnic media to reach their audience.
“Our strategy was to expand the electorate and ignite the base,” said Wilnelia Rivera, a political strategist who has long worked with Ms. Pressley. “We trained new activists to engage in a new form of political campaign and to reach the pool of people who don’t normally vote.”
Thomas Whalen, a social scientist at Boston University, said that Ms. Pressley’s victory represented a foreboding moment for machine politicians like Mr. Walsh.
“It’s a bad day for the gray heads in Massachusetts politics,” he said. “The political representation is starting to catch up with the demographics of the region.”
This was evident too in the Third Congressional District, north of Boston, where no fewer than 10 Democrats were competing for the open seat created by the retirement of Representative Niki Tsongas. The race was still too close to call on Wednesday and a recount was underway, but it had attracted a multicultural array of candidates, including five women, a man with a Korean and Lebanese heritage, recent immigrants, a gay man and a transgender woman.
“Pressley is lighting the path for minority groups, who now realize that if she can do it, we can do it too,” Mr. Whalen said. “That was one of J.F.K.’s political legacies. They said a Catholic could never be elected president.”
Katharine Q. Seelye reported from Boston and Matt Flegenheimer from Washington. Nicholas Fandos contributed reporting from Washington.