BOSTON — The battle for control of the Republican Party has reached deep-blue Massachusetts.

On one side of the GOP contest for governor is Donald Trump-endorsed Geoff Diehl, a conservative former state representative and failed U.S. Senate candidate who’s being advised by former Trump campaign manager Corey Lewandowski. On the other is Chris Doughty, a more moderate wealthy businessman and political neophyte who’s poured more than $2 million of his own money into his first campaign.

It’s a low-stakes race where the winner of the Sept. 6 primary is likely to lose to presumptive Democratic nominee Maura Healey, the state’s attorney general, in November. Yet the GOP contest is attracting attention from a growing cast of Republican characters with potential presidential ambitions — and turning a local face-off into a proxy war between the Trump wing of the party and more moderate New England Republicans fighting to keep their way of politicking alive.

Trump got involved back when it seemed like his Massachusetts nemesis, the popular GOP Gov. Charlie Baker, was going to run for a third term. But Baker, who doesn’t have an heir apparent, has stayed out.

Instead,New Hampshire Gov. Chris Sununu, one of the few moderate New England Republicans left standing, crossed the border to fundraise for Doughty this week. South Dakota Gov. Kristi Noem, a Trump ally who’s again being advised by Lewandowski after a brief split, is expected to stump for Diehl in Boston next week.

“This is about the future of the Republican Party as much as anything else,” Patrick Griffin, a Republican consultant who’s advised presidential campaigns and Sununu’s 2016 gubernatorial run, said in an interview.

“Kristi Noem’s got plans. Chris Sununu’s got plans,” he said. “This is all about standing up for where the party’s going and trying to direct it in a way or lead it in a way where we can win more elections, not less.”

But this is as much a battle for the future of the Republican Party as it is one for attention heading into 2024.

While Sununu gets plenty of play in his home state, fly-in politicians can get exposure in New Hampshire just by showing up in Massachusetts. The state is a media and money gateway to the first-in-the-nation primary state, offering would-be presidential hopefuls the chance to get on television screens in voter-rich southern New Hampshire and connect with deep-pocketed Massachusetts donors without the direct scrutiny that comes with stepping foot in the Granite State.

“There’s no sense in investing in lost causes,” said Colin Reed, who managed former Massachusetts GOP Sen. Scott Brown’s New Hampshire U.S. Senate campaign and worked on the 2008 presidential campaigns of Romney and John McCain. “But if you can use it to make a mark or increase your own name ID in a critical part of the country, as they say: there’s no interest like self interest.”

Republican New Hampshire Gov. Chris Sununu addresses racing fans at a NASCAR Cup Series auto race, July 18, 2021, in Loudon, N.H.