FIRST ON FOX: The political wing of a fiscally conservative political advocacy group with a powerful grassroots outreach operation is taking sides in a Republican Senate primary battle. The winner will move on to a race for a key swing state seat that the GOP aims to flip next year.

Americans for Prosperity Action (AFP Action) on Monday announced it is backing former Republican Sen. John E. Sununu’s 2026 bid to return to the Senate in the race to succeed retiring Democratic Sen. Jeanne Shaheen of New Hampshire.

The Senate battle in New Hampshire is one of a handful in next year’s midterm elections that will determine if the GOP is able to not only defend but possibly expand its majority in the chamber.

The endorsement of Sununu, who is facing off against former Sen. Scott Brown for the GOP nomination, was shared first with Fox News Digital on Monday.

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“John Sununu is exactly the kind of principled leader New Hampshire needs in the U.S. Senate,” AFP Action Director Nathan Nascimento said in a statement. “His deep roots in the Granite State and proven record of advancing limited government principles, cutting wasteful spending, and driving smart regulatory reform make him uniquely qualified to represent New Hampshire’s values in Washington.”

The endorsement by AFP Action is the third in 2026 Senate races, following their backing of former Republican National Committee chair Michael Whatley in North Carolina and former Rep. Mike Rogers of Michigan, who’s making his second straight Senate run. But it’s the group’s first endorsement in a Senate race where President Donald Trump remains neutral to date.

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Sununu is a former three-term representative who defeated then-Gov. Shaheen in New Hampshire’s 2002 Senate election. But the senator lost to Shaheen in their 2008 rematch.

Shaheen announced earlier this year that she wouldn’t seek re-election in next year’s midterms and Republicans are working to flip the seat as they aim to not only defend but expand their 53-47 Senate majority.

Now, after nearly two decades in the private sector, Sununu is returning to the campaign trail in New England’s only swing state.

It’s been 15 years since Republicans won a U.S. Senate election in swing-state New Hampshire. But Sununu is confident he can break his party’s losing streak.

“This is a race I know I can win,” Sununu said in a recent Fox News Digital interview. “It’s the right message, the right set of issues, and also the right person.”

Sununu is a brand name in New Hampshire politics. The former senator’s father, John H. Sununu, is a former governor who later served as chief of staff in then-President George H.W. Bush’s White House. And one of his younger brothers is former Gov. Chris Sununu, who won election and re-election to four two-year terms steering the Granite State.

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But Sununu won’t have a smooth path to the GOP nomination.

Brown, who was elected and served three years in the Senate in neighboring Massachusetts, and who, as the 2014 GOP Senate nominee in New Hampshire, narrowly lost to Shaheen during her first re-election, jumped into the race in late June.

“John can have all the support of the DC insiders and special interest groups in the world, and it won’t matter because New Hampshire primary voters know he’s not one of them,” Brown said in a statement to Fox News Digital. 

And Brown emphasized, “Like John, AFP has gone all-in on stopping President Trump. And like John, they have failed each time because they’re out of touch with our party’s base and relics from the past. History has a way of repeating itself, because New Hampshire voters are always smarter than the insiders give them credit for.”

Brown was referencing the 2024 Republican presidential primary endorsements of Trump rival Nikk Haley by both AFP Action and by Sununu.

AFP Action’s national and New Hampshire political teams met with both candidates before deciding to endorse Sununu.

“John E. Sununu is an unapologetic and proven champion of New Hampshire values like limited accountable government, personal responsibility and free markets. He is the perfect antidote for what’s wrong with Washington today and will make the Granite State proud in the U.S. Senate,” AFP regional director Greg Moore said.

AFP, the influential and deep-pocketed grassroots network founded by the billionaire Koch Brothers, highlights that in the 2024 election cycle, it and AFP Action engaged in a record-breaking 647 races, knocking on 20 million doors, and reaching 30 million voters. And the group says they expect “to significantly exceed those 2024 metrics across the board” in the 2026 cycle.

“We will put our unrivaled grassroots operation in full support of this effort and will work to ensure that this race becomes about the issues that matter most to New Hampshire residents and not about the political noise that has become a feature of politics lately,” Moore emphasized.

Republicans are working to expand their 53-47 majority in next year’s midterms. And Shaheen’s seat in New Hampshire is a top GOP target, along with battleground Michigan, where Democrat Sen. Gary Peters isn’t running for re-election, and Georgia, where Democrat Sen. Jon Ossoff faces a rough road to securing a second six-year term in the Senate.

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“We believe that this will be among the most competitive races nationally this year, and we feel that AFP Action can make a huge impact in getting John E. Sununu back in the Senate,” Moore said.

Ahead of AFP Action’s announcement, Brown landed the endorsement of former Republican Sen. Bob Smith of New Hampshire.

Sununu defeated then-Sen. Smith in the 2002 GOP Senate primary, and Brown topped Smith in the 2014 primary.

“I got to know Scott during the 2014 campaign when we ran against each other, and have come to appreciate his hustle, hard work and focus on New Hamsphire,” Smith said in a statement on Sunday.

The winner of next September’s GOP primary will likely face off in the general election with four-term Democratic Rep. Chris Pappas of New Hampshire, who is the frontrunner for his party’s Senate nomination.