HELENA, Mont. (AP) — Montana voters in Tuesday’s primary election will select a Republican challenger to three-term incumbent Democratic Sen. Jon Tester and candidates for an open U.S. House seat being vacated by far-right conservative Rep. Matt Rosendale.

Republicans have dominated recent Montana elections, leaving Tester increasingly vulnerable. They need to pick up just a couple seats in November to take control of the U.S. Senate.

For the primary, first-time candidate and former Navy SEAL Tim Sheehy is the choice of the Republican Party establishment, including former President Donald Trump and Montana Gov. Greg Gianforte.

The Belgrade businessman has sunk more than $2 million of his money into the race and is backed by major GOP donors. He faces two lesser known opponents.

On the Democratic side, Tester’s sole primary opponent has not reported raising or spending any campaign money.

The Tester and Sheehy campaigns already have been pounding each other on the airwaves in an advertising blitz that’s expected to intensify as November approaches.

Tester — a former state Senate president who’s considered a moderate in Washington — has emphasized his work for veterans and his roots as a third-generation farmer in central Montana. He’s also played up concerns that wealthy outsiders such as Sheehy, who came to the state in 2014, are buying up property and driving housing prices and taxes higher.

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Sheehy has sought to saddle Tester with public dissatisfaction over President Joe Biden’s struggles to stem illegal immigration on the southern border. And he’s appealing to supporters of Trump, who won Montana by 16 percentage points in 2020, by claiming in a social media post Monday without providing specifics that Tester supported the former president’s conviction last week in a New York hush money case.

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Tester won his three previous Senate races by slim margins.

The open U.S. House seat in solidly Republican, largely rural eastern Montana, features a seven-way GOP contest.

Contenders include former six-term former U.S. Rep. Denny Rehberg, state Auditor Troy Downing and state education Superintendent Elsie Arntzen.

Rehberg emerged from retirement and joined the race late after Rosendale launched a short-lived U.S. Senate campaign.

Downing was endorsed by Trump on Monday. He outraised the other primary candidates and touted his experience as auditor and running businesses in the private sector.

Arntzen, among the most conservative of the candidates, has leaned heavily into cultural issues such as her opposition to transgender girls participating in girls’ athletics.

Four candidates are seeking the Democratic nomination in the district. The winner will face long odds in November.

The state’s western House district, which includes the cities of Bozeman, Missoula and Butte, is expected to be more competitive in the general election.

Incumbent Republican U.S. Rep. Ryan Zinke, who served as Trump’s interior secretary, is being challenged by Mary Todd from the party’s right flank. Zinke narrowly won his 2022 primary.

Democrat and environmental attorney Monica Tranel, who lost to Zinke by 3 percentage points in 2022, is running unopposed in the western House district primary.

Gianforte is seeking a second term alongside Lt. Gov. Kristen Juras, while facing criticism for large property tax increases as property values increased. With a historic budget surplus following federal stimulus spending due to the COVID-19 pandemic, the state paid off its debt, reduced the top income tax rate and authorized up to $1,250 in one-time rebates to individual income tax payers.

Gianforte and Juras face a challenge from the right by state Rep. Tanner Smith, who represents part of Flathead County. His running mate, Randy Pinocci, is a public service commissioner from the Great Falls area.

In the Democratic primary for governor, former firearms executive Ryan Busse of Kalispell is running with attorney Raph Graybill. Helena attorney Jim Hunt is also seeking the gubernatorial nomination with running mate Jerry Driscoll.

Polls close at 8 p.m. Tuesday. Many voters already have cast their ballots by mail.

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Brown reported from Billings, Montana.