Capuano was the only Democratic incumbent in MA to lose a primary Tuesday night, with three others easily fending off challenges from the left.
Ayanna Pressley is heading to the US Congress in the latest remarkable upset in this year's primaries in advance of the November midterm elections.
Pressley is backed by Alexandria Ocasio-Cortez, the leftist socialist who defeated Crowley in NY on a message of pushing to "Abolish ICE".
"With so much at stake in the era of Trump, tonight's results make clear what Ayanna Pressley knew when she boldly launched her campaign against a ten-term incumbent: Change in the country and Congress can't wait", said Jim Dean, chair of the liberal group Democracy for America.
With her primary win in the safe Democratic seat, Pressley is now poised to become the state's first African-American elected to the House. But she made her background a major part of the race, highlighting the importance of boosting diversity in the Democratic Party, talking about her own experience with sexual assault, and regularly calling for more "bold, activist leadership".
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Our series, A More Perfect Union , aims to show that what unites us as Americans is far greater than what divides us. But what made Senator McCain so special was he cared about the substance of my heart rather than where I came from".
It is the only in the state to have a majority non-white population.
Capuano is now the fourth incumbent to fall in a primary election this year, joining Republican Reps.
However, two other Massachusetts Democrats, Reps.
MA senator Elizabeth Warren, a favourite to run in the 2020 Presidential election, was uncontested for the state's Democratic nomination. And while national progressives including Ocasio-Cortez rallied to her side, she had some strong local institutional support as well, including an endorsement from the Boston Globe. Ted Kennedy (D-Mass.), was an organizer for Sen.
Baker, a moderate who has been popular with voters in what is perceived as one of the nation's bluest states, will face Gonzalez, who served as secretary of administration and finance under Democratic Gov. Deval Patrick.
Another Democrat, U.S. Rep. Niki Tsongas, is retiring at the end of this term, and that open seat touched off a political scramble with 10 candidates on the Democratic primary ballot.