There’s an open congressional seat in Massachusetts where 10 candidates are waging war across a 34-town battlefield, each attempting to drown the others out on the airwaves as outside groups fan the flames and pot shots fly.

It’s quite the dogfight. Yet in a race overshadowed by devastating pandemic and an increasingly bitter primary battle between U.S. Sen. Edward Markey and U.S. Rep. Joseph Kennedy III, whose 4th Congressional District seat the candidates are running to fill, many of the hopefuls are struggling for air.

“People are mostly worried about their kids going back to school,” Democratic candidate and City Year co-founder Alan Khazei said. “So many people are undecided. Some are just starting to pay attention.”

The crowded Democratic field includes Khazei; Jake Auchincloss, a Newton city councilor and former Marine captain; Jesse Mermell, a former Brookline Select Board member and Gov. Deval Patrick aide; Becky Grossman, a former Middlesex County assistant district attorney and Newton councilor; former Wall Street regulator Ihssane Leckey; social epidemiologist Natalia Linos; attorney Ben Sigel, and tech entrepreneur Chris Zannetos. The victor will face the winner of the Republican primary between Julie Hall and David Rosa.

Much of the action has been on the Democratic side, where Auchincloss, who has distant ties to the Kennedy clan, has emerged a front-runner — and taken substantial heat because of it. He’s been blasted by his opponents over old, tone-deaf social media posts that included a reference to burning the Quran and taken to task over past comments concerning the Confederate flag and free speech. He’s also been criticized for a brief stint as a Republican helping to elect Gov. Charlie Baker.

“Criticism is a part of politics,” said Auchincloss, who’s apologized for the remarks and who touts his record as an “Obama-Baker” voter. “The more that your message is working with voters, the more other campaigns are going to direct criticism towards you.”

The action — and scrutiny — has been shifting toward Mermell recently, particularly after Dave Cavell, a President Barack Obama speechwriter, dropped out and pointedly endorsed her as the leading progressive against Auchincloss. Attorney General Maura Healey endorsed soon after. And Mermell’s long had support from close friend U.S. Rep. Ayanna Pressley.

“Given the dynamics of the race and where we are, it is time to support the progressive leader who’s best positioned to win,” Cavell told the Herald. “That’s Jesse.”

With the Democrats all hailing from Brookline, Newton or Wellesley, it’s hard for anyone to claim a geographical advantage similar to how Lori Trahan capitalized on her Lowell roots to win the seat vacated by U.S. Rep. Niki Tsongas in 2018.

The dearth of external polling means any candidate can claim momentum. The top tier is usually seen as some combination of Auchincloss, Mermell, Grossman, Leckey and Khazei. An outside poll released this week scrambled that slightly, tying Linos with Leckey and putting her ahead of Khazei, who narrowly leads the money race.

There’s some daylight between the candidates on the issues, particularly “Medicare for All,” which Leckey, Linos, Mermell said in a recent forum they support fully. Grossman and Sigel said they want a public option on the way to Medicare for All, Khazei and Zannetos want a strong public option and Auchincloss said he supports the Affordable Care Act.

But the overall lack of definition has led to a messy battle full of mudslinging across dozens of Zoom forums and candidates spending hundreds of thousands of dollars on television ads. Outside groups are backing Mermell. A Super PAC supporting Auchincloss is funded in part by his parents. Women Vote!, a Super PAC affiliated with Emily’s List, is running negative ads against Auchincloss and Khazei.