Two winning streaks are on the line in Tuesday’s Democratic Senate primary in Massachusetts.

Sen. Ed Markey has never lost an election in his nearly half century in elective politics – and the Kennedy dynasty remains undefeated in Massachusetts. One streak is bound to end.

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And in the western third of the state, Rep. Richard Neal, chairman of the powerful House Ways and Means Committee, is hoping to avoid the fate of Reps. Eliot Engel and Lacy Clay, two other longtime Democrats who were ousted earlier this year by much younger, progressive primary challengers.

In the Senate battle – which has grabbed national attention as it has turned increasingly bitter this summer – Markey closed out his campaign on primary eve with drive-in rallies in Worcester and Boston. "This race is about the future. It's about where do we go from here," Markey told supporters.

The former longtime congressman is running for a second six-year term in the Senate. The 74-year-old Markey was first elected to Congress in 1976, four years before the birth of his challenger, 39-year-old Rep. Joe Kennedy III.

Kennedy, a rising star in the Democratic Party, is the grandson of the late senator and U.S. Attorney General Robert F. Kennedy and grandnephew of the late President John F. Kennedy. The Kennedy family name still holds magic for many Massachusetts Democrats – and the congressman was the favorite when he launched his primary challenge nearly a year ago.

Markey surged this summer, taking a double-digit lead over Kennedy in four of the five most recent polls. But Kennedy and his campaign have pushed back against the latest surveys, saying the contest is much closer than the polls indicate.

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Even though he's 35 years senior to Kennedy, most of the latest surveys indicate Markey topping his challenger among voters 35 and younger.

While Kennedy's repeatedly urged voters to pick a "new" generation of progressive leadership, some of Markey's support among younger voters may be thanks to the backing of Rep. Alexandria Ocasio-Cortez, who stars in one of the senator's TV commercials.

The firebrand congresswoman from New York, the best known of the quartet of first-term progressive female House members of color known as "The Squad," last year endorsed Markey. The two lawmakers teamed up months earlier to produce and champion the landmark climate change proposal known as the Green New Deal.

And in recent weeks, Markey has also landed the backing of Democratic congressional candidates Jamaal Bowman of New York and Cori Bush of Missouri, the two progressive primary challengers who knocked off Engel and Clay.

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Markey also enjoys the support of the state’s other senator, Elizabeth Warren, who’s another rock star of the progressive movement.

Veteran Boston-based Democratic political strategist Mary Anne Marsh, who’s remained neutral in the primary showdown but whose firm works for the Kennedy campaign, noted that even though he was a senator and had been on the scene for decades, Markey wasn’t that well known in Massachusetts.

Marsh said Markey’s campaign “still had an opportunity to define him. And what they did was they made him the darling of the climate change warriors and instrumental to that was Alexandria Ocasio-Cortez… that brought in younger voters.”

Markey’s also faced criticism for spending too much time in the nation’s capital at the expense of his home state.

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“I’m running for the communities who don’t see their junior Senator outside of an election year. I’m running for the cities and towns that don’t have the luxury of accepting the status quo,” Kennedy tweeted this weekend.

But Marsh noted that Markey’s campaign “leaned into the fact that he was in Washington working all the time, legislating and putting his name on bills…They took the two big negatives and turned them into positives.”

The purported whitewashing of Markey’s record has frustrated Kennedy and his supporters. The four-term congressman – who was recently endorsed by House Speaker Nancy Pelosi – spotlights Markey’s votes supporting the 1994 crime bill, greenlighting the Iraq War and voting present on the resolution authorizing military force in Syria.

As the campaign hurled toward the finish line, the acrimony on both sides boiled over. Kennedy’s team called on Markey’s campaign to knock off online attacks directed at their candidate and his supporters, which included death threats.

Marsh said the incident “was really shocking to many people in Massachusetts.”

Pushing back, Kennedy recently accused Markey of questioning his family’s integrity, “weaponizing their history, appropriating their words. The senator’s time would be better spent reconciling his own history with the civil rights movement over the past 50 years…He has gotten it wrong over and over. So he attacks my family.”

The winner of the Democratic primary will be considered the overwhelming favorite in November’s general election. In the past half century, only two Republicans have won election to the Senate from Massachusetts.

While primary day is Tuesday, early voting by mail has been underway for weeks. Nearly half of those polled a recent Suffolk University survey indicated they were voting by mail.

In western Massachusetts, 31-year old Holyoke Mayor Alex Morse enjoys the backing of Ocasio-Cortez and the Justice Democrats – the progressive group that supported Bowman and Bush earlier this year – as he challenges Neal. The congressman, who has served 32 years in the House, is four decades older than Morse.

“After 32 years, Richard Neal knows how Washington works. But I want to change how Washington works,” Morse spotlights on his pinned tweet.

Neal enjoys the support of Pelosi – who at a news conference last week called him “an absolute leader in the Congress, a progressive leader in the Congress…People will say what they will say, but I know what he has done, and it would be a tremendous loss to that district to lose the chairman of the Ways and Means Committee.”

But Morse and his supporters charge that Neal’s blocked progressive legislation such as "Medicare for All."

Neal, showcasing his humble upbringing, recently touted that "I paid my last student loan payment in pennies, to remind myself of the struggle. I'm a living example of America's safety net, and I want that opportunity extended to every member of the American family."

A victory by Morse would send shockwaves through Washington, similar to Ocasio-Cortez’s 2018 primary upset of longtime Rep. Joe Crowley.

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Marsh noted that the “Markey-Kennedy Senate race is driving turnout – it has for the last few weeks and it certainly will on primary day. And that means a lot of progressives are coming out. That certainly hurts Neal and helps Morse.” But she added that “if Neal runs up big margins in the cities of Springfield, Holyoke and Pittsfield, the math doesn’t work for Morse.”

The winner of Tuesday’s primary is guaranteed a direct ticket to Capitol Hill – as no GOP candidate is running in the Democratic-leaning district.