Edward Markey

Not just that, but Markey went conspicuously further than fellow Democrats on other issues, including in his proud support for impeaching President Trump a third time — a prospect that Moulton, and top Democratic congressional leaders, have downplayed.

Most notably, Markey leaned into the issue of transgender rights more than perhaps any other high-profile Democrat running this year. Of course, Moulton’s controversial comments about trans youth in sports after the 2024 election became a weakness Markey regularly exploited. But in the process, Markey staked out a staunch position — vocally backing a Massachusetts law that protects transgender student athletes — that other Democrats have avoided.

“I ran on Medicare for All. I ran on the Green New Deal. I ran on taxing millionaires and billionaires. I ran on slashing the defense budget,” Markey said at a post-primary event in Malden on Wednesday. “Massachusetts sent a resounding message that a progressive vision is the correct message for the voters of not only Massachusetts but for our country.

“That,” Markey said, “is the winning message in 2026.”

Taken together with Markey’s campaign alliances with national figures like Vermont Senator Bernie Sanders and New York Representative Alexandria Ocasio-Cortez, the playbook looks similar to how Markey weathered a reelection challenge from Joe Kennedy III in 2020.

This time, however, the success of Markey’s progressive strategy helped him buck a national trend that claimed some of his congressional colleagues: At least seven other Democratic incumbents lost their seats this year amid a party-wide reckoning over aging leadership. And it comes months before Democratic presidential hopefuls begin kicking off their campaigns to court the party faithful — making it a potential late barometer that voters are looking more for progressive bona fides than merely new faces.

At Markey’s primary night party Tuesday, few attendees spoke of his 50-year-long career in Washington. Instead, they lauded his efforts to protect abortion rights, his vocal support for immigrants, and his commitment to the LGBTQ community.

To the uninitiated, they could have been talking about any progressive Democrat, 80 years old or otherwise.

Markey’s win was an “exclamation point” on a 2026 primary season that showed “progressives are the dominant political force within the Democratic Party,” said Joseph Geevarghese, executive director of Our Revolution, a leading grass-roots progressive group that backed the senator.

The result, he added, “captures how hungry the grass roots are for transformational change.”

“If you want to run for president and win the nomination in 2028, you’ve got to be a bold progressive,” Geevarghese said. “I don’t think there’s any other way to be competitive.”

Progressive backers of Markey emphasized how the senator’s case was broader than simply putting up vehement opposition to Trump — a strategy he shared with other successful upstarts in this primary season. Moulton tried to burnish his credentials with the base by arguing he would be tougher on Trump than Markey, and critiqued him for voting for some Trump appointees.

In Massachusetts and elsewhere, “candidates pushing for big structural changes and channeling anger not just about Donald Trump but about the broader state of the economy performed pretty well despite being massively outspent,” said Dan Geldon, a longtime top adviser to Senator Elizabeth Warren. Warren, too, was a key early Markey endorser.

“In the presidential context, big money interests will have a ton of sway as they always do, but it’s obvious from the past year that Democratic voters don’t think things are going well or that Trump is the only problem,” he said.

Of course, Markey’s unabashedly progressive campaign wasn’t the only factor behind trouncing Moulton across nearly every corner of the state. The senator’s 30-percentage point margin of victory was in line with late polls of the primary, which had increasingly begun to point to a Markey blowout — not a tighter race that seemed to be unfolding earlier in the summer.

The 47-year-old Moulton staked his campaign on a confidence that primary voters would fire Markey simply for being too old. He claimed to be just as progressive as the senator — but that rang hollow after years of positioning himself as a pragmatic, center-left voice of reason within the party.

His increasingly pointed attacks on Markey, such as suggesting he was implicated in the Epstein files, not only turned off voters but underscored the lack of a strong, cohesive idea behind his campaign aside from “generational change.”

Rachel Ramirez, a stay-at-home mom from Lynn, said at a polling place on Tuesday that she voted for Markey because his interest in policies that support families and immigrants outweighs any concerns about his age.

“Regardless of age,” she said, “you have to vote for people who align with your values.”

Even those who voted for Moulton did not take much issue with Markey’s progressive platform, nor did they express broader concerns about the party moving left.

While Markey “has done a good job for a very long time, it’s time for a change,” Sarah Almer, 50, said at a Cambridge polling place Tuesday.

Still, Tuesday was a good night for incumbents in Massachusetts, not just progressives. US representatives Richard E. Neal and Stephen F. Lynch, both of whom have more moderate records than Moulton, each dispatched younger, left-wing challengers — though Neal had the closest call of his 19-term career against first-time candidate Jeromie Whalen.

Though Moulton ended up a weak challenger, Markey once again deftly sensed where the center of gravity among primary voters was.

Political strategist David Axelrod attributed Markey’s success to his early pivot on issues that voters have also moved left on: Medicare for All, the concentration of wealth that has captured Washington, and environmental issues.

His “progressive coat of armor” strategy worked in 2020 against Kennedy, said Axelrod, who served as a top adviser to former President Barack Obama.

It wasn’t lost on some Moulton supporters that Markey campaigned yet again on enacting big progressive promises, which for the most part have failed to become reality. Markey argued that former President Joe Biden’s Inflation Reduction Act, a sweeping climate bill, contained many provisions in his Green New Deal plan.

At Markey’s primary night party at Boston’s Omni Parker House — a decidedly old-school venue and birthplace of the Parker House dinner roll — the room was young, diverse, and energized.

“There is no age limit on doing the right thing,” state Senator Lydia Edwards, an East Boston Democrat, told the crowd. “In Massachusetts, we do not throw away wisdom because it comes with gray hair and cool sneakers.”

Kelly Garrity of the Globe staff contributed to this report.