Dan Koh, former White House aide to President Joseph R. Biden Jr., won the Democratic primary in Massachusetts’ Sixth Congressional District on Tuesday. Koh defeated a crowded field, including progressive state representative Tram Nguyen and businessman John Beccia, to secure the open seat.

Koh is the only Democratic congressional candidate this year endorsed by both President Biden and former Vice President Kamala Harris. The race opened after moderate Democrat Seth Moulton, who challenged Senator Ed Markey, lost his primary. Koh highlighted his connections to Biden and former Labor Secretary Marty Walsh during the campaign.

Koh raised significantly more funds than his rivals, spending $2.4 million on advertising compared to Nguyen’s $158,000 and Beccia’s $3.2 million. Koh defended Biden’s fitness during the race, stating he was never concerned about the President’s decision-making. If elected in November, Koh would become the first Asian American to represent Massachusetts in Congress.

The district leans heavily Democratic, making Koh a clear favorite against Republican Micah Jones in the general election.