It’s hard to say who’s the frontrunner in the race for Massachusetts’ only open congressional seat.

Dan Koh — one of six Democrats running to represent Massachusetts’ 6th Congressional District, which comprises the northeastern corner of the state — has the the most money and the backing of some of the country’s best-known Democrats. John Beccia has the catchiest name and a prodigious ability to self fund his candidacy. And state Rep. Tram Nguyen has picked up late-breaking momentum thanks to some big recent endorsements.

Still, there are no external, impartial surveys that could indicate which candidates are leading, and which ones are struggling to connect with voters.

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Another metric — fundraising — suggests a separation into clear tiers.

At the highest end, Koh, an advisor to President Joe Biden and former chief of staff to then-Boston Mayor Marty Walsh, had raised $4.7 million and had nearly $2 million left in the bank as of August 12, while financial technology executive and consultant Beccia had raised $4.5 million (mostly from loaning his own money to the campaign) and had about $750,000 left to spend down the race’s home stretch.

Nguyen sits in a middle tier of her own, with about $900,000 raised and roughly $190,000 left to spend.

Then come three candidates grouped together at the bottom: software engineer Bethany Andres-Beck, former state representative and Maternal Mental Health Leadership Alliance founder Jamie Belsito, and veterinarian and former congressional and State Department staffer Mariah Lancaster. Still, all three have raised enough money — from the high $200,000s to the high $300,000s — to be considered viable. (When Alexandria Ocasio-Cortez was first elected, she raised roughly $300,000 to fund her run against incumbent New York U.S. Rep. Joe Crowley.)

The picture’s even murkier considering that, with such a crowded field, a candidate could theoretically eke out a victory with just 17% of the vote.

We’re identifying six major factors that are likely to sway the primary’s outcome.

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How much hostility to Trump is enough?

Each of the candidates pitches themselves as opposed to Trump and his administration’s policies. But how strongly they’re hitting that message varies.

Asked to synopsize his pitch to voters, Koh told GBH News: “Right now we are in a unique moment where we have a president who’s destroying our democracy, seems to get worse every day, and after the midterms we’re going to have at least two more years of this man. So I think in this unique moment, we need someone who’s a fighter with experience at all levels of government to take on this president on Day 1, stop his destruction of democracy and lower costs for people.”

Koh’s focus here is clearly on defending democracy from Trump, with “lower[ing] costs” almost a footnote. Contrast that to Beccia, whose quick-hit pitch puts affordability first.

“The system is broken, and we can’t keep sending the same people to D.C.,” Beccia told GBH News. “People can’t afford to live. People can’t have jobs, get jobs, can’t get health care.”

He wants to bring down costs, create jobs and improve access to education and health care — including “scaling back the damage that’s been done by the Trump administration, including things like cutting SNAP benefits and the problem of food insecurity that is rampant in our state.”

Next to Koh’s pitch, Trump looks more like an afterthought.

It’s not clear which approach will be more appealing to 6th District voters: a candidate who’s focused on fighting an existential battle against Trump, or one who emphasizes making life more affordable.

Koh isn’t the only candidate striking a strong anti-Trump note.

“I’ll defend democracy with every fiber of my being,” Nguyen said. “My father served with Americans during the Vietnam War. We came from across the world to the U.S. for democracy and freedom and opportunity, and you can bet that those are the things I’m going to fight to keep.”

On their website, Lancaster accuses Trump of “gutting our government, kidnapping our friends and neighbors, and selling off our country to the highest bidder.”

On their website, Andres-Beck calls Trump “[t]he biggest threat to our country.”

And Belsito, on her website, warns that Trump is “openly planning to stay in power for an illegal third term.”

Does momentum trump money?

Koh and Beccia are the race’s runaway leaders when it comes to fundraising, and Koh has a huge advantage when it comes to money left in the bank.

But in the run-up to the election, Nguyen — a former legal-aid lawyer who came to the United States from Vietnam as a child, grew up in public housing and calls herself an “unapologetic progressive” — is enjoying an enviable hot streak.

She’s recently been backed by Massachusetts Attorney General Andrea Campbell, current U.S. Reps. Ayanna Pressley and Lori Trahan and by the Boston Globe’s editorial board, which touted her life story and noted that she’d be the first Asian American elected to Congress from Massachusetts if she wins. (The same goes for Koh, who the Globe described as voters’ next-best option.)

Do voters want an “establishment” Democrat?

After his service in Boston City Hall, Koh worked as an assistant to Biden for two and a half years, and the president clearly holds Koh in high esteem. The former president effusively endorsed Koh in May, saying he would be a “one heck of a congressman” and telling him, in classic Biden fashion, ”Go get ’em, pal.”

But does Biden’s backing pack a punch? And if so, does it pack the same punch it would have before the last election cycle, when he exited the presidential race at the last minute?

Koh has also been endorsed by Vice President Kamala Harris and Transportation Secretary Pete Buttigieg.

The extent to which Biden’s support boosts Koh could depend on how many independent voters decide to participate in the Democratic primary. While recent polling shows that Biden remains popular among Democrats, with a favorability rating of 78%, he’s far less popular among independents, with just 27% viewing him favorably.

Either way, it’s a strong reminder that Koh has already spent time in Washington, D.C. — a point he clearly believes works in his favor.

Will dissatisfaction with U.S. support of Israel be a meaningful factor?

In the Sixth District contest, Belsito stands out for her forceful frustration over Israel’s war in Gaza.

According to a Pew poll from April, about 8 in 10 Democrats and Democratic-leaning independents currently hold unfavorable views of Israel, compared to just 5 in 10 in 2022.

Belsito, who was the first Arab American elected to the Massachusetts Legislature, said she’s criticized what she calls the “U.S.-funded genocide in Palestine” for years.

“I was told by the Democratic Party I should have kept my mouth shut, and I’d never be able to run for office again,” she said, adding: “I don’t want my tax dollars going to murder moms and babies on a livestreamed genocide on Instagram.”

It’s not a part of Nguyen’s quick campaign pitch, but she, too, has pledged to work to halt all military funding to Israel as it carries out what she refers to on her campaign site as a “genocide in Gaza.” (Belsito accuses Nguyen of coming late to this position, a charge Nguyen denies.)

Lancaster — who worked in the State Department to combat the illicit trade in animals and other natural resources — also criticized Trump for “supporting U.S. complicity in genocide.”

And Andres-Beck states, on their campaign site, that they’ll “work for a future of freedom and dignity for all Israelis and Palestinians and end U.S. support for apartheid and genocide.”

What about AI?

Andres-Beck says, when they greet voters, they tell them: “My name is Bethany Andres-Beck. I’m a software engineer from Middleton. And I want to regulate AI so it works for all of us.

“That’s how we start, and then we have a conversation from there,” Andres-Beck added.

Their experience working with tech, they argue, makes them especially qualified to respond to the rise of artificial intelligence and propose effective regulations.

“The thing that I bring that no other candidate and no current congressperson has is, I’m a working software engineer. I can ... provide real oversight over how our government is using these new technologies, sometimes against us,” they said.

That could tap into what is — in the eyes of Bay State residents — a concerning issue of our current moment. A recent survey found that 82% of Massachusetts voters think that, without regulation, it’s very or somewhat likely that AI will create serious risks, and that support for robust state-level AI regulations is overwhelmingly high.

This is good news for Andres-Beck, who was the only member of the field to announce their candidacy before Moulton announced his primary challenge to Democratic Sen. Ed Markey.

It could also be a bit of a drag on Koh, who’s been the beneficiary of more than $600,000 in spending by Think Big PAC, which “support[s] Democratic candidates dedicated to advancing AI innovation in America.”

But artificial intelligence isn’t a major issue Koh digs into in his campaign materials, and it’s likely that only a small share of primary voters will even know about this campaign-finance factor.

Will the race be a referendum on Moulton?

Ask the people hoping to succeed Moulton what they thought of his time in office, and you’ll get a wide range of answers. Nguyen praised Moulton and his “incredible team” for terrific constituent services, while also saying that she’ll make a point of soliciting policymaking input from a broad swath of constituents if elected.

Framed this way, the implication seemed to be that that’s something Moulton didn’t do.

Koh said he respects Moulton and his representation of the district — then added that he wants everyone he represents to have his cellphone number, which is printed on his campaign fliers.

“What I would want to do most importantly in Congress is to be present and have people be able to approach me on any issue,” Koh said. Once again, the suggestion seemed to be that Moulton took a different tack.

Most blunt, perhaps, was Lancaster, who said of Moulton: “I think that one of the most important things about working in the House of Representatives is knowing how to work well with others. And where I see Congressman Moulton having struggled is at that point.”

As the candidates set themselves apart from Moulton — and from each other — they may offer some clues of where the Democratic Party is heading as it seeks to return from the political wilderness. Primary day is Tuesday, Sept. 1.