Elections officials could have preliminary tally Thursday in Fourth District race, as Auchincloss leads Mermell

Wellesley Assistant Town Clerks Liz Kelley (left) and Alissa Keene (right) counted the remaining ballots that were received by 8 p.m. on Tuesday and have not yet been counted in the race for the Fourth District. The counting took place in the Great Hall at Wellesley Town Hall.Jonathan Wiggs/Globe Staff

Jake Auchincloss, a Newton city councilor who ran as a centrist in a heavily progressive field, opened up as much as a 1,700-vote lead Wednesday in the Fourth Congressional District’s still-unsettled Democratic primary, where local officials were planning to count hundreds of more ballots.

A Suffolk Superior Court judge on Wednesday approved a petition from Secretary of State William F. Galvin to allow officials in at least three communities to tally roughly 1,450 votes that had gone uncounted amid a deluge of mail-in ballots.

Elections officials could have a complete preliminary tally in the primary as early as Thursday, adding clarity to what has become a two-way race between Auchincloss and Jesse Mermell, a former Brookline selectwoman.

But whether the votes will ultimately sway the results is unclear. Unofficial returns within the nine-way field seeking to succeed Joseph P. Kennedy III showed Auchincloss had built a 1,506-vote lead over Mermell with 96 percent of precincts reporting.

With more than 148,000 ballots already counted, just one town, Franklin, had yet to report any results, according to unofficial results updated Wednesday.

Auchincloss, a former Republican who won wide support in more moderate communities dotting the district’s southern end, had captured 22.4 percent of the vote to Mermell’s 21.4 percent. The Associated Press, which tallies the unofficial results, had yet to declare a winner.

Still, a spokeswoman for Galvin said preliminary figures the office has reviewed suggest the gap is even wider between the two candidates, at roughly 1,700 votes — a deficit that would further mute the impact of the outstanding ballots.

Franklin had roughly 600 ballots that had yet to be counted, according to Galvin’s office. Newton, where Mermell had run up a winning margin, had 751 uncounted ballots, and Wellesley, another town where Mermell prevailed according to preliminary results, had roughly 100. Officials in each town are expected to tally them by Thursday, according to Galvin’s office.

David A. Olson, Newton’s city clerk, said that the 751 mail-in ballots had all arrived between 5 p.m. and when polls closed at 8 p.m., on Tuesday, but that he was instructed by Galvin to “hold” them as his office sought the court approval. Olson said his office also has roughly 500 additional ballots that have been counted but have yet to be added to its preliminary count, which also could happen Thursday.

In filing the court petition, Galvin said in a statement that it is “important that we preserve that same level of transparency for ballots counted after Election Day” as those counted on it. He said his office also had been in contact with Auchincloss’s and Mermell’s campaigns.

Mermell early Wednesday had questioned whether the preliminary results pouring in from the district’s 34 cities and towns reflected every vote cast, saying in a statement that it was “too soon for anyone to declare victory or stop counting” given tens of thousands of voters had cast ballots by mail for the first time under the state’s newly expanded voting law.

Her campaign released a letter it sent to local clerks Wednesday asking them for more detailed information about the ballots the municipalities had on hand, including the number of provisional ballots. In the letter, Katie Prisco-Buxbaum, Mermell’s campaign manager, also raised the specter of seeking a recount, saying it was important to have the “more robust” data “before any decision is made on further counting requests.”

Under state law, a campaign can file a petition by Friday, with at least 500 signatures, for a districtwide recount if the margin between first and second place is within 0.5 percent. A campaign can also ask for more narrow recounts at the precinct or city ward levels, needing to file only 10 signatures with each request.

“We think the answers to these questions are important before any campaign or media outlet declares a victor in this race,” Prisco-Buxbaum wrote.

Doug Rubin, an adviser to Auchincloss, said the candidates should let the process play out.

“Jake feels that any vote that came in before 8 p.m. yesterday should be counted,” Rubin said.

Becky Walker Grossman, a Newton city councilor, was holding in third place with 26,756 votes, far behind Auchincloss, at 33,216, and Mermell, at 31,710, with about 4 percent of precincts left to report.

Mermell, a progressive onetime aide to former governor Deval Patrick, handily won in Boston’s deep-blue suburbs, taking Brookline by thousands of votes and topping the more moderate Auchincloss in his hometown, according to unofficial results.

But Auchincloss corralled wide support along the South Coast, where he and an outside super PAC backing his candidacy had blanketed towns and cities with ads and Auchincloss heavily invested time campaigning.

Mermell and other progressive candidates also appeared to carve up votes elsewhere, including in Attleboro, where she finished outside the top three vote-getters despite earning the endorsements from the city’s legislative delegation.

Julie Hall, of Attleboro was projected to beat David Rosa, of Dighton in the district’s Republican primary. Whichever Democrat emerges will be heavily favored on Nov. 3 in a district that Hillary Clinton won by 24 points in the 2016 presidential election and Barack Obama by 16 points four years earlier.

The Democratic race is the last unsettled open-seat primary in the country.

Grossman, Brookline social epidemiologist Natalia Linos, former Wall Street regulator Ihssane Leckey, and attorney Ben Sigel each posted social media messages Wednesday thanking supporters and conceding the race. The field also included City Year cofounder Alan Khazei.

Auchincloss, a self-described “Obama-Baker” voter, pitched himself as a pragmatic choice with a focus on clawing federal funds back to the district and being a partner to the state’s popular Republican governor, Charlie Baker.

Once a Republican who worked for the state GOP and Baker’s 2014 campaign, Auchincloss often found himself playing defense in the unwieldy Democratic field, either for past controversial comments or his emphasis on opposing President Trump, with fellow candidates and outside groups targeting him alike.

Mermell, meanwhile, repeatedly framed her candidacy against that of Auchincloss, holding up what she billed as a long progressive track record on the Brookline Select Board, working for Patrick, and heading a left-leaning business group.

The 40-year-old Brookline resident also drew the backing of several of Massachusetts’ Democratic stars, including Representative Ayanna Pressley, a longtime friend, and Attorney General Maura Healey. And two primary candidates — Dave Cavell, of Brookline and Christopher Zannetos, of Wellesley — who ended their campaigns but remained on the ballot also threw their support behind Mermell, as she tried to separate herself from other progressive candidates in Leckey and Linos.

But in many voters’ minds, it was difficult to parse what generally were similar liberal policy positions among several liberal candidates.

The field as a whole endorsed expanding health care, though Mermell, Linos, and Leckey outwardly backed a single-payer system such as Medicare for All. Several candidates pushed for tightening gun control measures. And all but Zannetos and Auchincloss said they endorse ending qualified immunity for police facing threats of lawsuits; the other two said they support reforming it.