SEEKONK, Mass. (WPRI) — Newton City Councilor Jake Auchincloss has won the Democratic primary to replace Joe Kennedy in the 4th Congressional District, eking out a narrow victory in a crowded field despite an onslaught of negative advertising and his own past work as a Republican campaign staffer.

The Associated Press called the race for Auchincloss at about 1:30 a.m. early Friday, more than 48 hours after polls closed, when some laggard communities — notably Franklin — finally finished counting ballots under the close supervision of Secretary of State William Galvin.

“I’m honored that the people of the Massachusetts 4th District have chosen me as the Democratic nominee for Congress,” Auchincloss said in a statement released immediately after the AP called the race. “We won 25 of the 34 cities and towns across the district, a testament to the strong, full-district campaign we built.”

He linked his own success to that of his grandfather, whom he described as “a poor Jewish kid” who walked into a Marine recruiting office just after the U.S. entered World War II and wound up getting a college education thanks to the G.I. Bill.

Unofficial results showed Auchincloss leading former Brookline Select Board member Jesse Mermell by about 2,000 votes out of over 150,000 cast in the primary, giving him 22% of the vote, with the other five Democratic candidates trailing behind. He will face Republican nominee Julie Hall, a former Attleboro city councilor, in the November election.

Mermell called Auchincloss on Friday morning to concede the race, releasing a video message to her supporters at noontime making it official. She acknowledged it was a “tough day.”

“I won’t be filing for a recount. But that doesn’t mean that I’m content with the returns,” she said. “I have serious concerns about some gaps in the process that came to an end early this morning.”

She added, “If the ranked-choice voting campaign needs a new face — give me a call, guys. I’ve got some time on my hands.”

Auchincloss is expected to address his supporters in Newton on Friday afternoon.

Auchincloss emerged as the central figure in the 4th District primary during the summer. The 32-year-old Harvard graduate and U.S. Marine Corps combat veteran proved to be a strong fundraiser and hammered home a message focused on economic development and opposing President Trump. He was aided by a big-spending super PAC funded in part by his wealthy family, and he got the highest-profile media endorsement in the race when The Boston Globe backed him.

“His track record in local government and his military background as a former Marine captain provide depth of experience and perspective that are valuable assets as Congress navigates crises in public health and the economy,” the Globe editorial board members wrote in their endorsement.

None of the other hopefuls “have as much promise as Auchincloss,” they argued.

Among a group of hopefuls who all hailed from Brookline and Newton, Auchincloss prioritized outreach to communities in the southern part of the 4th District, particularly Fall River, that lacked a favorite-son candidate. That effort paid off with endorsements from Mayor Paul Coogan of Fall River and Mayor Jon Mitchell of New Bedford — the latter of which isn’t even in the 4th District.

He also avoided left-wing positions, refusing for example to endorse a Medicare for All single-payer system. That frustrated progressive activists, who agreed they didn’t want him to win the nomination but could never coalesce around a single alternative.

Still, Auchincloss faced relentless attacks from his opponents — including a deep-pocketed super PAC linked to the Democratic group Emily’s List — who cast him as a moderate and a political opportunist who had briefly joined the GOP when he worked to elect Republican Gov. Charlie Baker. They drew attention to various social media comments he’s made over the years and his free-speech defense of Newton students who flew the Confederate Flag. (He apologized for some of his actions.)

As it became clear the eventual 4th District winner would likely need barely 20% of the vote to come out on top, the primary grew enormously expensive. The candidates themselves had already spent $4.7 million as of Aug. 12, while outside groups have poured in at least $2.16 million, according to a ProPublica analysis of Federal Election Commission filings.

Auchincloss previously worked at Solaria Labs, an arm of the insurer Liberty Mutual. He and his wife Michelle, who works at the consulting firm Bain & Co., welcomed their first child, Teddy, earlier this year.

Ted Nesi ( is WPRI 12’s politics and business editor and a Target 12 investigative reporter. He is a weekly panelist on Newsmakers and hosts Executive Suite. Follow him on Twitter and Facebook