A POLITICAL UPSET

Massachusetts votes for change

Capping off an improbable rise from the Boston City Council to the threshold of Congress, Ayanna Pressley made history Tuesday night by defeating U.S. Rep. Michael E. Capuano in a closely fought Democratic primary. The resounding victory clears the way for Pressley, whose chances were discounted when she decided to take on a 20-year incumbent, to become the first black woman ever to represent Massachusetts in Congress.

It’s a milestone to behold, especially given the obstacles she overcame. Pressley went into the race with fewer resources and without the blessing of the Democratic establishment. Boston Mayor Marty Walsh, former Gov. Deval Patrick and even some of her council colleagues quickly closed ranks behind Capuano. The two had few concrete policy disagreements, and supporters of Capuano pointed to his long voting record as a reliable supporter of progressive causes.

But Pressley — who became the first woman of color elected to the City Council and then compiled an impressive record reforming the hidebound liquor licensing system — convinced voters to expect more. She made the case that the Seventh Congressional District — which the Legislature drew specifically as a majority-minority district — needed a representative with a more intimate understanding of its needs. Capuano, a former Somerville mayor, brought home billions from Washington. Pressley convinced voters that it was just as important what a representative brought to Washington.

And her victory carries an unmistakable message, amplified by Tuesday’s other electoral upsets further down the ticket: Massachusetts politics is changing. Candidates aren’t willing to wait their turn anymore. The power of incumbency is weakening.

The campaign “dared to do what Massachusetts Democrats aren’t supposed to do,” Pressley, 44, said in her victory speech.

Pressley’s insurgent campaign should be a wake-up call to the old guard. Her victory is a political earthquake, and there will be aftershocks. New political alliances have been formed, anchored by a new guard of female politicians who stood by Pressley, notably Attorney General Maura Healey and Boston City Councilor Michelle Wu.

The new reality — that officeholders should expect challengers — should encourage politicians to stay on their toes and take nothing for granted. At the same time, the success of challengers like Pressley should entice anyone who’d ever contemplated a primary challenge in Massachusetts.

Run. It’s a new world, and you don’t have to wait. Just ask Ayanna Pressley.

FROM AN EDITORIAL IN THE BOSTON GLOBE