Lori Trahan

The Democrats’ endorsement of the Andover state legislator — announced two days after early voting began and many others voted by mail — is also something of a rejection of the primary’s five other candidates, including its leading fund-raiser and one of its perceived front-runners, Dan Koh.

Koh, a former Biden White House aide, narrowly lost to Trahan in the Third District’s open primary in 2018, and considered challenging her two years later. His hometown of Andover was later redistricted into the Sixth, where Koh has touted national support, including from Biden, in his bid to replace Representative Seth Moulton.

Koh has put his federal work front and center, pitching to voters that it would help him deliver for the North Shore-anchored district. But Trahan, a former congressional chief of staff before she won her seat, said she doesn’t “think it’s necessary that you understand the D.C. ecosystem” going into Congress, pointing to others who, like Nguyen, “cut their teeth in state legislatures.”

Trahan and Pressley, both of whom first won their House seats in 2018, are two of only three women in the state’s nine-person House delegation. (House minority whip Katherine Clark is the other.) Either Nguyen or Koh would be the first Asian American to represent Massachusetts in Congress, if elected.

“Tram Nguyen is a barrier-breaker, table-shaker, and exactly the kind of progressive leader this moment demands,” Pressley said in a statement.

“I’ve known Tram for almost a decade now,” she added, “and what inspires me most about her is her contagious optimism and how she believes deeply in what our Commonwealth and our country can achieve when we demand more from our leaders and government.”

Nguyen, in a statement, said she has “deeply admired” Trahan and Pressley’s work “fighting for a stronger, more inclusive future built on progressive values.”

“I am honored to have them standing with us and look forward to working alongside them in Congress to build a powerful movement ready to challenge the status quo,” she said.

The endorsements come at a critical time for Nguyen. Her campaign launched its first TV advertisement late last month, emphasizing her background as an immigrant and that in 2018, she ousted a conservative Republican state representative to win a seat on Beacon Hill.

But Nguyen and her campaign have lagged others in fund-raising, and urged supporters in a recent social media post to “chip in today to help us keep our ad on the air.” Her latest financial report shows she spent $325,000 from the beginning of July through Aug. 12, and had about $190,000 on hand entering the final three weeks ahead of the Sept. 1 primary.

That number pales in comparison to her better-funded opponents. Koh, who spent about $1.8 million during the same period and still had nearly $2 million on hand, also reported pouring in $150,000 more of his own money late last week. John Beccia, a Lynnfield fintech executive who is largely self-financing his campaign, spent about $2.3 million during the same timeframe and had $750,000 on hand.

Still, Nguyen is getting a boost from at least two outside groups: Save America Fund, a Rhode Island-based super PAC that reported shelling out almost $88,000 this year on Nguyen’s behalf. In recent days, Pro-Choice Majority Action, a PAC that focuses on helping Democrats, has reported pouring $450,000 into digital ads backing Nguyen.

Nguyen, like Koh and other candidates this cycle, has given messaging cues to outside groups using a tactic known as “red-boxing,” in which candidates publicly post suggestions to follow. The discrete instructions allow them to flout rules preventing coordination with super PACs, which can raise and spend unlimited amounts of money.

She’s also nabbed endorsements from unions, including United Auto Workers International, and liberal activist groups like Progressive Massachusetts, and touted the backing of at least 50 sitting state representatives and senators.

There hasn’t been any independent public polling in the race. The other Democrats running include Bethany Andres-Beck, a Middleton software engineer; Jamie Belsito, Topsfield town moderator and a former state representative; and Mariah Lancaster, a Salem veterinarian and former congressional aide.

Trahan didn’t directly address whether her endorsement of Nguyen was, in part, a bid to block Koh from Congress. But she said she knows “something about being outspent in races like this” — Koh also out-raised her by more than $500,000 in their 2018 race — and plans to knock doors for Nguyen to reach voters in the primary’s final stretch.

“This has been a really interesting election cycle, where candidates with the most money have not necessarily won in these primaries,” said Trahan, who co-chairs the House Democratic Policy and Communications Committee and has campaigned for other Democrats across the country. “So I think people are paying attention to the candidates and how they’re going to be different.”

Kelly Garrity of the Globe staff contributed to this report.