Democratic voters in Massachusetts will decide the futures of Sen. Edward J. Markey, Rep. Joseph P. Kennedy III and House Ways and Means Chairman Richard E. Neal in the Bay State’s congressional primaries Tuesday. 

Big donors, outside groups and high-profile endorsements have fueled the much-anticipated contests, which in deep-blue Massachusetts prove more pivotal than the general election and essentially will determine who will head to Capitol Hill for the 117th Congress.    

The main spotlight has been on Kennedy’s challenge of Markey, who is seeking a second full term in the Senate after serving decades in the House. Neal, who is in his 16th term, faces Holyoke Mayor Alex Morse in the closely watched 1st District race that has drawn spending from outside influences including industry-aligned groups for Neal and progressive organizations boosting Morse.

Rep. Stephen Lynch, who is seeking his 10th full term in Massachusetts’ 8th District, also has a primary challenge from physician Robbie Goldstein, though political observers in the state believe Lynch is less at risk than Neal or Markey. 

So far this cycle, eight incumbents, including three Democrats, have lost renomination. 

With much on the line Tuesday, here are four things to watch:  

1. AOC vs. the Speaker

When Kennedy, in his fourth term representing the suburban Boston 4th District, jumped into the Senate race last year, early polling had him with a double-digit lead that made Markey one of this year’s most vulnerable senators. That was no surprise, given that he’s a scion of what amounts to an American political dynasty. 

But polling earlier this year showed the race tightening, as Markey shored up his support among the party’s progressive wing.  

Markey has taken a lead in more recent polls, after winning endorsements from progressive stars, especially New York Rep. Alexandria Ocasio-Cortez, a prolific grassroots fundraiser who cut an ad for the sitting senator this summer. Sen. Elizabeth Warren, the state’s other senator and another powerhouse of the progressive movement, got behind Markey, as did several other senators and progressive organizations. 

Earlier this month, Speaker Nancy Pelosi offered her endorsement of Kennedy, saying in a campaign email: “He knows that to achieve progressive change, you must be on the front lines leading movements of people. Massachusetts and America need Joe Kennedy’s courage and leadership in the Senate.”

2. What’s in a name?

Though Kennedy had his family name, his service in the House and his youth (he’ll turn 40 in October), Markey, who is 74, seems to have captured the progressive left. 

“One of the things that really struck me is Markey’s ability to leverage his Green New Deal sponsorship and AOC endorsement into kind of a new persona for him as a kind of outspoken progressive,” said David Hopkins, a political science professor at Boston College, who writes the politics blog Honest Graft. 

Peter Ubertaccio, a political scientist at Stonehill College in Easton, Mass., agrees.

“The Kennedy campaign provided Markey an opportunity to amplify his voice,” he said. “Markey can be a somewhat awkward politician — he doesn’t have the star power of Elizabeth Warren. He’s very much a creature of Capitol Hill, but progressives view that in the best way, that he’s carrying a policy torch.”

3. Show me the money

Not only has the Kennedy-Markey race been a draw for political money, but so, too, have the Neal-Morse contest and the crowded race to succeed Kennedy in the 4th District.

Markey reported more than $3.5 million in the bank as of Aug. 12, while Kennedy was down to about $1.4 million. Outside groups have poured more than $6.5 million into the Senate primary, according to federal disclosures, including a Kennedy-supporting super PAC dubbed the New Leadership PAC and a pro-Markey effort called United for Massachusetts.  

Political money has been a leading campaign issue in the 1st District, where Neal’s long history of corporate PAC contributions has been a featured criticism. An outside group dubbed Fight Corporate Monopolies notified the FEC in July that it was dropping $150,000 on a TV ad opposing Neal. An ad posted by the group online says that “Corporate power is corrupting democracy. And Richie Neal is part of the problem.” 

The American Hospital Associations PAC has invested heavily on behalf of Neal, while progressive groups, such as Justice Democrats, which has supported a number of other primary challengers including New Yorkers Ocasio-Cortez in 2018 and Jamaal Bowman’s upset over Foreign Affairs Chairman Eliot L. Engel this year, have spent to boost Morse. 

“The 1st District race is really emblematic of what we’re seeing in many races, last cycle and this cycle, where the establishment-backed Democrat, backed by corporate PAC contributions, that’s Neal, and then Morse is aligned with the more progressive groups,” said Sheila Krumholz, executive director of the Center for Responsive Politics, a nonpartisan group that tracks political spending. 

It’s notable that both Markey and Kennedy swore off corporate PAC money last year, though they had previously collected such donations. 

“We’re seeing strong threads that have been shaping races on the left for some time now and appear to be continuing if not strengthening,” Krumholz added.   

Morse, who is 31 and openly gay, seems to have weathered allegations that he made unwanted advances toward college students. He fits the profile of a younger, more progressive challenger to Neal, who is 71. 

4. The race to replace Kennedy

Members of the crowded field of Democratic contenders to replace Kennedy in the 4th District have also been raising piles of money.

Nine candidates are on the ballot with no clear front-runner, and five of them have hauled in more than $1 million.

Newton City Council member Jake Auchincloss and Jesse Mermell, a former aide to then-Gov. Deval Patrick, are among those candidates, along with Alan Khazei, a founder of the education nonprofit group City Year; Becky Grossman, at-large city councilor in Newton; and Ihssane Leckey, a former special examiner at the Federal Reserve.

Khazei had more than $640,000 cash on hand as of Aug. 12, while Leckey held about $365,000 in the bank. Auchincloss disclosed holding about $353,000 in campaign money as of that date; Grossman had about $350,000; and Mermell’s campaign reported about $281,000.

Political insiders say they are not sure how the race will shake out.

“That’s probably the only real cliffhanger we have,” Ubertaccio said.