They’re both Marines, 40-somethings, and waging generational fights. So why aren’t Seth Moulton and Graham Platner allies?

US Representative Seth Moulton built a national profile by bucking fellow Democratic leaders and helping dozens of fellow veterans turn once-red congressional seats blue.

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That makes Moulton’s current political pursuit — running for US senate —very much on brand, with one seeming exception: Neither Moulton nor his vets-focused PAC has endorsed Graham Platner, a fellow military veteran who captured attention by — stopif this sounds familiar — bucking fellow Democratic leaders and trying to turn a red Senate seat blue.

As Moulton makes his own case to take US Senator Ed Markey’s seat, he has simultaneously backed nearly a dozen service members across the country — all of whom are running for US House, not Senate — but has declined so far to support the one running for a Senate seat widely viewed as the best pickup opportunity for Democrats this fall.

Like Moulton, Platner is a US Marine. And like Moulton, the 41-year-old oysterman is waging his political future on uprooting a longtime New England incumbent — in his case, 73-year-old US Senator Susan Collins of Maine — with a pitch built on generational change.

“Look, he’s a veteran running in an important race, so although we don’t often get involved in Senate races, we are considering it,” Moulton told the Globe.

Still, his decision to date not topublicly support Platner’s campaign, even while praising him, has spotlighted a clash between two images of Moulton, 47. There’s the figure who has often supported more moderate Democrats with service backgrounds and elevated his national profile in the process. Then there’s Moulton, the Senate candidate, who has embraced more progressive positions since challenging US Senator Ed Markey — seemingly aligning closer with the populist Platner.

Before this cycle, Moulton’s PAC had endorsed at least 10 US Senate candidates since 2018.

“They should be allies,” said Tony Cignoli, a Massachusetts-based Democratic strategist, noting how Massachusetts Democrats often stump for like-minded candidates in New Hampshire or Maine. An “attachment” with Platner, he added, could boost Moulton’s own campaign, given the attention Platner has generated both in New England and nationally.

Platner becamethe presumptive Democratic nominee in his race after Maine Governor Janet Mills bowed out last month. Moulton acknowledged there are “definitely some parallels” between the two, and said a cross endorsement — in which Moulton or his Serve America PAC backs Platner, who then also lends his public support to Moulton against Markey — was “maybe” on the table.

There appear to be some mixed signals between the campaigns. Platner’s campaign, for its part, said Platner has no intention of endorsing in the Massachusetts Senate primary. And days after Moulton spoke with the Globe, his campaign sent a statement, saying “there is no cross-endorsement.”

On paper, Platner has the resume that organizations like Serve America have celebrated in their quests to install servicemembers among the ranks of Congress.

Many similar left-leaning veterans-focused organizations sprang up after President Trump’s first election in 2016, fueled by protests over what they viewed as Trump’s attacks on democracy.

Moulton’s PAC alonehas backed 38 successful Democrats since 2017, 24 of whom flipped their districts from Republican control. This year, it has endorsed 11 candidates, none of whom are candidates for Senate. Several of its alumni have eventually captured other seats, including US Senator Elissa Slotkin of Michigan and Virginia’s Abigail Spanberger and New Jersey’s Mikie Sherrill, both of whom won their states’ gubernatorial races last year.

Moulton is personally motivated by“encouraging the Democratic Party to do even a little bit more to bring veterans into the party,” said Matt Chilliak, Moulton’s former campaign manager.

The congressman has spoken of his experience with post-traumatic stress disorder and lobbied for increased mental health services.He also frequently appears on TV criticizing Trump’s military strategy.

But translating the themes on which Moulton built his national profile into a successful statewide campaign in Massachusetts has proven more difficult. “If you’re going to be a senator, you need to take up a wider array of positions” beyond veterans-focused issues, Chilliak said.

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It’s a different approach from Markey, who fended off a challenge in 2020 by elevating his climate change work, prompting an army of young progressives to rally on his behalf. A similar uprising of support for Moulton has not sprung up.

“Seth has to talk about what he learned in the Marines in terms of political leadership,” said Emily Cherniack, founder of New Politics, another group that recruits service members to run for office,who urged Moulton to run for the House in 2014. “And voters will decide if it’s time for a new generation of leadership.”

Moultonis personally involved in Serve America’s endorsement process. The organization considers three main criteria when deciding to endorse: how a candidate talks about their service, if they’re running in an important race, and whether they can win — criteria Platner appears to meet.

Platner’s campaign platform includes planks to pay service members a fair wage and to defend federal Veterans Affairs programs. He speaks of struggling with post-traumatic stress disorder after his service, at times growing emotional while speaking of the support he received.

And when Platner faced scrutiny last fall following headlines about his past social media posts and a tattoo resembling a Nazi-affiliated symbol, Moulton said he believed Platner should stay in the race, saying he “very much represents a new generation of leadership.”

“Look, as a Marine veteran myself, he is far from the first Marine I’ve met who got a tattoo that he didn’t fully understand,” Moulton told NBC10 in October.

He latertold CNN he would be open to backing Platner, even as other members of Congress — including US Representative Jake Auchincloss, another Marine veteran — disavowed the upstart candidate over his past comments and tattoo.

Other veterans organizations have stepped up for Platner.

Common Defense, which bills itself as the nation’s largest grassroots membership organization of veterans and military families, has backed Platner, as has Veterans for Responsible Leadership, which endorsedMoulton in January.

Scott Peoples, executive director of Veterans for Responsible Leadership, said his organization waited in part because the organization’s members have a “pretty diverse background,” and they wanted to speak with Platner multiple times about his past “mistakes.”

“We’re looking for people who are willing to stand on the principles they have, and Graham really believes what he believes in,” Peoples said.

“As veterans, we’ve met people that have gone through personal struggle and made some mistakes and sought help and admitted faults,” he added, “and as long as you give people that grace, we feel that can make you a stronger leader.”

Moulton is competing for attention in his own race. He’s railed against the so-called gerontocracy in Washington and embraced more progressive positions, such as calling to “abolish ICE” and returning money donated to him by AIPAC, apro-Israel group.

Markey’s supporters are aiming to make the race about who is the true progressive candidate. A super PAC backing the incumbent beganrunning an ad last month targeting Moulton’s record on issues, including immigration enforcement and the Green New Deal, casting him as insufficiently progressive.

Arguably, it’s not Moulton but Markey who most aligns with Platner’s staunchly progressive, anti-corporate politics.

Indeed, when Platner visited the US Capitol in March, he met with one person in the primary: Markey, according to the senator’s office.

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Sam Brodey of the Globe staff contributed to this report.