A generational shift in politics finally arrives in Mass.

Ayanna Pressley (left), Maura Healey, and Mike Capuano.Globe staff photos

FEEL THE TREMORS? Attorney General Maura Healey’s endorsement of Ayanna Pressley over US Representative Michael Capuano is another sign that the old-guard white male establishment that has controlled the Democratic power structure since forever is finally starting to crack.

Pressley, the first black woman to win a seat on the Boston City Council, is still the underdog in this race. But, win or lose, she represents the party’s new face. It’s smart politics for Healey to endorse her over Capuano. There’s also an element of reciprocity since, four years ago, Pressley endorsed Healey over Warren Tolman, the establishment favorite Healey beat in her own race.

But Healey’s endorsement shows something more than political shrewdness or old-school loyalty. A generational shift in politics is finally arriving in Massachusetts, powered by the conviction that it’s OK to challenge an incumbent or establishment darling. And you don’t have to be a woman to do it. Boston City Councilor Josh Zakim is taking on Bill Galvin, who’s now in his sixth term as secretary of state.

Of course, there’s pushback. Scientists don’t know exactly what noise dinosaurs made, but when in pain, they probably sounded a lot like former US representative Barney Frank complaining that Pressley’s run represents “politics at its most egotistical.” In an interview a few months back, Frank, who served in Congress from 1981 to 2013, also said that when Capuano decides to retire is when others should vie for his seat.

But Healey is betting today on the next generation, which is essentially her own. The AG is 47, Pressley is 44, and Capuano is 66. No doubt the longtime congressman, who was first elected to the House in 1998, still greets every day fired up and ready to fight for liberal causes he has championed for decades. He boasts a long list of endorsements from labor and progressive organizations. But, at a certain point, a fresh face may be preferable to voters simply because it’s fresh. When you’re on the other side of that equation, it feels unfair. But Capuano can’t change his date of birth. All he can do is argue his years in Washington add up to seniority that benefits his district and party, especially if Democrats take control of the House.

Pressley’s campaign to unseat Capuano got a big boost when Alexandria Ocasio-Cortez shocked national Democrats by beating longtime incumbent US Representative Joseph Crowley in a New York congressional primary race. There are surface similarities between Capuano and Crowley, in that both are 20-year incumbents challenged by a woman of color. But as others have noted, Capuano, unlike Crowley, isn’t taking the race for granted. He’s campaigning hard, and has won the endorsement of the Congressional Black Caucus PAC and former governor Deval Patrick, not to mention Mayor Marty Walsh of Boston. Pressley, meanwhile, has won endorsements from three female colleagues on the Boston City Council — Annissa Essaibi-George, Kim Janey, and Michelle Wu; Damali Vidot, the president of the Chelsea City Council; and all four women who serve on the Cambridge City Council.

In endorsing Pressley, Healey identified issues they have worked on together — “from fighting profiling and discrimination by Boston nightclubs to protecting students from predatory, for-profit schools and helping survivors of sexual trauma, domestic violence and human trafficking. She stood by me and supported me in my first campaign, at a time very few elected leaders were willing to take a chance on an outsider candidate like me.”

An incumbent who ends up winning has the power to punish disloyalty like Healey’s. And Capuano can certainly pull out a victory. But Healey isn’t worrying about that. She’s with Pressley. At the very least, that will make Capuano look back over his shoulder as he races toward primary day and the ground shifts under his feet.