Rarely do election upsets fit so neatly into an ongoing political narrative as the one that took place in Boston on Tuesday night when a Boston city councilor, Ayanna Pressley, threw out a 20-year congressman, Rep. Michael E. Capuano (D), in Massachusetts’s Democratic primaries.

Policywise, there isn’t much daylight between the two politicians. But in terms of the factions of the party they represent, they couldn’t be farther apart.

She had little-to-no Democratic Party establishment support. He had the backing of the city’s mayor, fellow Massachusetts members of Congress and Democratic leaders in Congress such as the head of the Congressional Black Caucus, Rep. John Lewis (Ga.).

She was the first black woman to serve on the Boston City Council. He is white and represents a majority nonwhite district in Boston.

She had the support of the current leader on the far left of the party, Alexandria Ocasio-Cortez. He did not.

Pressley’s primary win is the second-most-notable congressional win on the left this year since Ocasio-Cortez dethroned one of the leaders of the Democratic Party, Rep. Joseph Crowley, in the New York primaries. If Ocasio-Cortez’s win in New York City was a wake-up call for Democratic leaders that the party’s base is agitated and motivated for a shake-up in the Trump era, Pressley’s win confirms the trend.

Her win over Capuano comes a week after Florida Democratic voters nominated someone for governor who wants to abolish the Immigration and Customs Enforcement agency, Andrew Gillum.

Ayanna Pressley is the Democratic nominee for Congress in Massachusetts’s 7th District. She became the first black congresswoman from Massachusetts on Nov. 6. (Amber Ferguson/The Washington Post)

All three of these newcomers to the national Democratic scene have a few things in common that allow us to lump them into what seems to be a growing and formidable faction of the Democratic Party: They are people of color. They have at least one or two policies that put them further to the left on the spectrum than the establishment candidates they’re challenging. (In Pressley’s case, she didn’t accept super PAC money, and she supports abolishing Immigration and Customs Enforcement.) And they unseated or beat out white, older candidates who make up the party establishment.

This movement is centered on the congressional level, and so far it is taking place in solidly liberal congressional districts like New York City and Boston. (Gillum’s gubernatorial nomination in a swing state is a whole different ballgame. But champions of this movement claim this is the beginning of a strategy that the Democratic Party should have deployed in the 2016 elections: Move unapologetically to the leftward, more populist poles of the party, because that’s where the people are.

It helps, activists say, that the candidates this movement is putting forward couldn’t be more of a contrast to President Trump in their policies and background. The Democratic Party is nominating women and people of color at historically high rates this election cycle. “We just have this percolation, this synergy, this transcendence happening in 2018 that people are responding to,” Nina Turner, head of Our Revolution, a group spun out of Bernie Sanders’s presidential campaign, said after Gillum’s win in Florida.

In her victory speech Tuesday night, Pressley called Trump a racist: "Our president is a racist, misogynistic, truly empathy-bankrupt man," she said.

Whether the seemingly paradoxical strategy to move to the left to win over Trump voters is a winning strategy remains to be seen. Of the big wins on the left so far, only Gillum in Florida and Stacey Abrams, the gubernatorial nominee in Georgia, are positioned to put it to the test. Ocasio-Cortez and Pressley should easily win the general election in their heavily Democratic districts; so would have the members of Congress they beat.

But it’s notable that, two years after Sanders’s presidential campaign, the energy on the left is alive and well — and kicking out longtime members of Congress.