FIRST ON FOX: Former Republican Sen. Scott Brown is building a campaign war chest as he prepares for a likely grueling Senate primary battle in New Hampshire against former Sen. John E. Sununu, in a crucial 2026 race where the GOP aims to flip a longtime Democrat-held seat.

Brown, the first major Republican to jump into the race to succeed retiring longtime Democratic Sen. Jeanne Shaheen, reported on Tuesday that he hauled in over $1.2 million in fundraising during his first full quarter as a candidate, according to figures shared first with Fox News Digital.

Shaheen's open seat is one of the GOP's top targets as the party aims to not only defend but expand its current 53-47 majority in the Senate.

The total from the July-September third quarter of 2025 fundraising includes money brought in by Brown's Senate campaign as well as a joint fundraising committee formed with his Leadership PAC, Strong Country for Today and Tomorrow. 

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According to the figures, Brown had nearly $900,000 cash on hand at the end of last month.

Brown, a former senator from neighboring Massachusetts and the 2014 GOP Senate nominee in New Hampshire who later served as U.S. ambassador to New Zealand in President Donald Trump's first administration, called the fundraising response "overwhelming."

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"With this strong showing, our campaign will have the necessary resources for the long haul, and allow me to campaign the only way I know how: relentless hard work and a focus on retail politics that Granite State voters expect."

And pointing to four-term Democratic Rep. Chris Pappas, who is considered the clear frontrunner for his party's Senate nomination, Brown emphasized, "New Hampshire always knows better than Washington, D.C., and that’s a message I intend to prosecute against Congressman Pappas and anyone else who decides to enter this race."

Brown's comment about "anyone else" is a reference to Sununu, who's expected to launch a campaign this month, setting up a likely bruising primary battle for the GOP Senate nomination in New Hampshire.

"I'm sure that if we put together a strong team, this is a race that can be won. This is a race I know I can win. And more importantly, it's a role where I know I can make a difference for New Hampshire," Sununu said last month in a Fox News Digital interview.

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Sununu, a former three-term congressman who won election to the Senate in 2002 before losing his 2008 re-election bid, reiterated he would "make a decision in October" on whether to launch a Senate campaign. 

"It's a winnable race for the right person who reflects our state's values, not the values of Washington," Sununu told Fox News.

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.

Republican state Sen. Dan Innis, a longshot for the GOP nomination, ended his campaign last month after Sununu publicly said he was considering a Senate run. Innis said he would back Sununu and also urged Brown to end his campaign.

But Brown, long known as a tireless and scrappy campaigner, has made it very clear that he has no intention of suspending his campaign.

And he's repeatedly taken aim at Sununu over the former senator's lack of past support for Trump, who holds immense clout over the GOP.

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Sununu, along with then-Gov. Chris Sununu, endorsed former ambassador and former South Carolina Gov. Nikki Haley in the 2024 New Hampshire Republican presidential primary, as she battled Trump for the nomination. 

And on the eve of the first-in-the-nation presidential primary, the former senator wrote an opinion piece titled "Donald Trump is a loser," that ran in the New Hampshire Union Leader, the state's largest daily newspaper.

"@JohnSununu was the original 'Never Trumper,'" Brown charged in a social media post last month. "He's going to have to explain that."

In recent radio appearances, Brown also reminded listeners that Sununu "called President Trump a loser."

And pointing to Sununu's past decade and a half in the private sector, Brown has highlighted that his likely primary rival "was lobbying for the special interests."

Brown endorsed Trump ahead of his 2016 New Hampshire primary victory, which launched him toward the GOP presidential nomination and ultimately the White House. Brown later served as U.S. ambassador to New Zealand during Trump's first term.

Trump, whose endorsement in Republican primaries is extremely influential, has remained neutral to date. 

But the president may be willing to overlook Sununu's past jabs.

Earlier this year, when Chris Sununu flirted with a Senate bid after leaving office, Trump urged him to run.

The younger Sununu, who was Haley's top supporter and surrogate in New Hampshire, repeatedly criticized Trump during the 2024 Republican presidential primaries.

Trump told reporters in April that he had met with the former governor in the Oval Office and that he'd "support him fully."

"He’s been very nice to me over the last year or so," Trump added. "I hope he runs. I think he’ll win that seat." 

And a national Republican familiar with the Senate race in New Hampshire told Fox News Digital last month, "President Trump appreciates winners and understands that John E. Sununu puts this race on the map for Republicans."

Fundraising, along with polling, is a key metric of a candidate's strength and popularity, and the money raised can be used to build a campaign team, and pay for ads and grassroots outreach efforts.