FALL RIVER, Mass. (WPRI) — The fierce Democratic primary battle to succeed Congressman Joe Kennedy shifted into a higher gear on Thursday, as one candidate dropped out to endorse a rival in an explicit effort to avoid splitting the progressive vote.

David Cavell, an Obama administration alum and former assistant attorney general, suspended his campaign on Thursday morning after tepid fundraising and weak poll numbers. He immediately endorsed Jesse Mermell, a former Deval Patrick adviser who is trying to consolidate progressive voters.

In a joint interview with WPRI 12, Cavell made no bones about his calculus: he said he feared the crowded field of candidates would allow Newton City Councilor Jake Auchincloss to win the Democratic nomination in the 4th Congressional District, which stretches from northern Fall River through the Attleboros and Taunton up to the wealthy Boston suburbs.

“Jake is the elephant in the room — and pun intended there,” Cavell said — a shot at Auchincloss’s days as a registered Republican working to elect GOP Gov. Charlie Baker.

“We need somebody who’s going to fight for progressive values in Congress,” Cavell said. “We need somebody who’s going to represent this district the way that it deserves to be represented. And in a race that doesn’t have ranked-choice voting, where you only need about 20% to win, I felt like I couldn’t be a part of preventing that from happening.”

Cavell was one of three high-profile endorsements that Mermell picked up on Thursday, along with Planned Parenthood, where she previously worked, and Attorney General Maura Healey, who is Cavell’s former boss.

“We were already feeling strong coming into today, but we’re certainly feeling even stronger with 19 days left to go and our ever-growing coalition,” Mermell said.

“We’re not a campaign that’s funded by corporate PAC checks or fossil-fuel money, not by self-funding,” she said. “We’re raising good money, we’re raising what we need to compete, but we were never going to have the most. What we are having, and counting on, is having the muscle and the hard work and the coalition that’s going to put us over the top on Sept. 1.”

Mary Anne Marsh, a longtime Democratic strategist in Massachusetts, called Cavell’s move “a major development” in the 4th District race.

“I think this helps Jesse Mermell try to make this a one-on-one race,” she said. “That has to be her goal here.”

“If she can make this a one-on-one race with Jake, then she’s got a real shot here in terms of winning,” Marsh said. “She clearly hasn’t raised the money everyone else has — or at least that top tier — but I think she’s got all the endorsements of people who really get people out, work the doors, work the phones, do all of that, which you really need.”

Auchincloss has come under increasing attack from his opponents as his well-funded campaign appeared to surge, particularly since he won the endorsement of The Boston Globe — a sign of how seriously they are taking him.

During a campaign stop in Fall River on Thursday, Auchincloss declined to respond directly to Cavell. “We’re a nation in crisis right now,” he said. “My focus is not on the other eight campaigns. My focus is on cities like Fall River, Attleboro, Taunton. … We need to get federal relief for state and local budgets. We need to get a Main Street relief act.”

Auchincloss was joined by Fall River’s mayor, Paul Coogan, who endorsed him the same week as The Globe. With Attleboro Mayor Paul Heroux remaining neutral and Taunton now led by a Republican, Coogan was viewed as one of the biggest potential endorsements that could help a candidate from Newton or Brookline make inroads in the 4th District’s Bristol County communities.

Coogan said there were multiple strong candidates in the 4th District primary, but the 32-year-old Marine Corps veteran stood out. “I look for someone that can bring the district together,” Coogan said. “A lot of the same issues that Fall River faces, that Taunton faces, that Attleboro faces, are the same issues Jake faced in Newton.”

It’s far from clear that Auchincloss and Mermell are headed for a two-way race, though.

One of Auchincloss’s fellow Newton city councilors, Becky Grossman, has pumped $429,000 of her own money into her campaign and blanketed the airwaves with messages aimed at parents and seniors. There has been no independent polling in the race, but a trio of internal surveys — one by Grossman’s own campaign and two by the campaign of Ihssane Leckey — have all showed Grossman in front, albeit with under 20% of the vote.

“As three different polls have shown Becky in the lead, it’s clear that her message is meeting the moment,” Alex Vuskovic, her campaign manager, said in an email. “Becky’s running with the fierce urgency of a mom who is ready to take on Big Pharma, the NRA, and Trump Republicans.”

Grossman also remains well-funded, with $290,000 in cash on hand available as of Wednesday, according to her campaign. The Auchincloss, Mermell and Leckey campaigns all declined to reveal their current fundraising numbers.

Meanwhile, Leckey has emerged as a potentially significant roadblock to Mermell’s efforts to dominate among progressives.

A former Federal Reserve regulator, Leckey had put $800,000 of her own money into her campaign at last check, airing TV ads that link her with icons of the party’s left like Bernie Sanders and Alexandria Ocasio-Cortez. Her fundraising got a boost earlier this week when Fox News host Tucker Carlson criticized her on prime-time TV.

“Ihssane has surged over the last month with a bold call for change that is resonating with voters who want to continue the trend of sending strong, progressive women of color to Congress,” said Leckey spokesperson Josh Miller-Lewis. “In just one month, she doubled her grassroots fundraising total from the second quarter and is the only progressive in the race who can defeat Jake Auchincloss.”

Leckey criticized Mermell on Thursday after Politico highlighted a new super PAC has formed to boost her. But Leckey has faced her own controversy in recent days, as the Boston chapter of the Democratic Socialists of America threatened to rescind its endorsement due to a letter alleging she mistreated former campaign workers. Leckey denies the allegation and told the group she no longer accepts its endorsement.

“It’s hard to say where the state of the race is right now,” said Shannon Jenkins, a political science professor at the University of Massachusetts Dartmouth. She noted that a recent poll conducted by Leckey’s campaign had such a wide margin of error that “it’s impossible to distinguish between the top four candidates” — meaning Grossman, Auchincloss, Leckey and Mermell.

“Ultimately, I think the race is wide open: 25% of voters are undecided according to the Leckey poll,” Jenkins added. “The endorsement from The Globe may help Auchincloss, although the controversy surrounding that endorsement may negate some of the boost he might have expected to get from that.” (The Globe editorial board received blowback from some readers due to Auchincloss’s GOP past and controversial social media statements.)

Time is running short: not only is the primary less than three weeks away, but most voters are expected to cast a ballot by mail, meaning some are already making their final decisions now. Analysts say the uncertainty surrounding how turnout will be affected by mail voting — as well as high interest in the marquee Sept. 1 contest between Kennedy and U.S. Sen. Ed Markey — makes it nearly impossible to feel confident about predictions in the primary.

At the same time, four other 4th District Democrats are still campaigning in an effort to manufacture a late-breaking burst of support that pushes them into the top tier. They will get another opportunity to make their cases on Tuesday evening, when Stonehill College hosts a virtual debate to which all eight remaining candidates have been invited.

City Year co-founder Alan Khazei, who has made previous unsuccessful runs for statewide office, raised $177,000 from July 1 to Aug. 12 and has $363,000 available for the final stretch of the primary, according to his campaign. He has already made a major investment in TV advertisements, and his aides have indicated they expect to make more announcements soon.

“Our campaign is extremely energized by a surge of support over the last few weeks,” said Khazei spokesperson Keyon Rostamnezhad. “Alan’s message of putting People Before Politics has been strongly resonating with the 60,000 constituents we’ve called.”

Ben Sigel, a Wellesley attorney who jumped into the primary in January, has emphasized that he would be the first Latino to represent Massachusetts in Congress. In a statement Thursday, he made clear he had no intention of following Cavell’s lead to help clear the field for Mermell or another hopeful.

“We are still pressing on,” he said. “Team Sigel is committed to this race and is charging towards September 1st.” (His campaign did not respond to a question about its current financial resources.)

Chris Zannetos, a tech entrepreneur, has also been airing TV ads. His spokesperson, Christen Baglaneas, said his fundraising has “accelerated” since July 1 and he expects to have roughly the same amount of cash on hand — about $500,000 — that he did at the start of the summer.

“As I bike around the district, voters constantly tell me that we have to find a way through hyper-partisan gridlock to make our economy work for everyone, not just those at the top,” Zannetos said in a statement. “Now that we are in the final sprint, I’m looking forward to talking with the voters about how I’ve proven myself to be the best candidate to do that.”

Dr. Natalia Linos, an epidemiologist, was the last Democrat to enter the primary, doing so in May and linking her decision to the need for medical expertise in Congress to combat the coronavirus pandemic. Her campaign said it raised $123,000 since July 1 and has about $168,500 in cash on hand for the primary.

“We’re launching our first TV ad this week and are getting ready for a Weekend of Action on Aug. 15 and 16 with sign waves or flyer drops planned in all 34 cities and towns, and will reach an additional 15,000 voters through text and phone banking on just those two days alone,” Linos campaign manager Erin Gregor said. “This team is fired up and ready to keep building the movement for science-based leadership right through Sept. 1.”

Peter Ubertaccio, a political science professor at Stonehill, said Thursday was a good day for the Mermell campaign, describing an endorsement from Maura Healey as “a gold standard in Massachusetts Democratic Party circles.” But the 4th District candidates will continue to struggle to shift voters’ attention away from the presidential campaign and the Markey-Kennedy clash.

“It’s probably a wide open race at this point,” Ubertaccio said.

Ted Nesi (tnesi@wpri.com) 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