Dan Koh, who worked as a White House aide during the presidency of Joseph R. Biden Jr., won the Democratic primary in a solidly blue Massachusetts congressional district on Tuesday, according to The Associated Press, topping a crowded field that pursued an open seat.
In a costly race in the state’s Sixth Congressional District, Mr. Koh defeated rivals including Tram Nguyen, a progressive state representative who as a child fled Vietnam with her family as political refugees, and John Beccia, a largely self-funded businessman who ran as an outsider.
Mr. Koh is the only Democratic congressional candidate this year endorsed by both Mr. Biden and former Vice President Kamala Harris. While many Democrats are seeking to turn the page on the Biden administration and the party’s 2024 election defeat, Mr. Koh highlighted his connections.
“You will be one heck of a congressman,” Biden said in a phone call that was released by Mr. Koh’s campaign in May. “Everything you and I fought for, everything we did to help ordinary people, is in jeopardy now in this administration, so we got to get you elected.”
The race in the Sixth Congressional District, which spans the state’s North Shore, opened up after Representative Seth Moulton, a moderate Democrat, declined to seek re-election and instead challenged Senator Ed Markey. Mr. Moulton lost his primary on Tuesday night.
