Washington — Montanans are voting Tuesday in primaries for a key Senate seat that Democrats are fighting to hold onto come November, kicking off a general election brawl for control of the Senate. 

Incumbent Democratic Sen. Jon Tester is expected to face off against entrepreneur Tim Sheehy, with both men all but certain to win their party's nomination in Tuesday's primaries.

Tester, 67, was first elected to the upper chamber in 2006. The Democratic incumbent is known as a rural farmer with deep ties to the Big Sky State — and two fingers on one hand from an accident with a meat grinder. He's billed himself as a moderate, sometimes breaking with his party's slim Senate majority. And his seat is among a handful that Democrats are fighting fiercely to defend in the upper chamber. 

On the other side of the aisle is Sheehy, a former Navy SEAL and founder of an aerial firefighting company who has become the clear frontrunner among a handful of Republicans seeking the nomination. The 38-year-old Minnesota native has the backing of the bulk of the party, with endorsements from Sen. Steve Daines, Montana's other senator, a Republican, who isn't up for reelection this cycle, along with former President Donald Trump.

Trump endorsed Sheehy in February, when a surprise entrance into the GOP race threatened to complicate Sheehy's path to the nomination. Rep. Matt Rosendale, who launched an unsuccessful bid against Tester in 2018, had entered the race, threatening to divide the party. But within a week, he withdrew, as Trump said Sheehy "is the candidate who is currently best-positioned to DEFEAT Lazy Jon Tester, and Regain the Republican Majority in the United States Senate."

The race in red Montana, a state where Trump beat President Biden by more than 16 points in 2020, is expected to be among the most competitive and costly this cycle. The state has elected Tester to the Senate three times, though he's the only Democrat serving in statewide office in Montana at present. And Montana's changing political profile poses a major hurdle for Tester's reelection.

Eric Raile, a political science professor at Montana State University, says the political demographic in the state has been changing, noting that trends suggest that an influx of new residents in the state is made up largely of Republicans. The change adds to a dominant showing by the GOP in the state in the last two elections, as Raile noted that their "trajectory has been really strong."

Tester has been able to overcome his party affiliation in the past, winning three relatively close elections in the state and bucking trends in the process. But with the shifting demographics in the state, the calculations for the Democrat this year appear different.

"He's had some tough races, he's won them all," Raile says. "But he does run as a moderate. I think this campaign is shaping up to be a little bit different in that sense, because he's running farther to the right than he has in the past, and he probably needs to do that."

For Tester, that shift can be observed in the way he's broken with some of his party on issues like border security, talking about the economy and opposing Chinese land buying in the U.S., among other things. And he's distanced himself from President Biden in the process. Raile says the effect has been that what Tester is saying is not all that different from his opponent. 

"If Tester is going to occupy that ground, his campaign appears to be saying, 'people like Jon Tester, and if he says Republican-like things, Republicans and some independents aren't going to have a lot of reasons to disagree with him and vote against him,'" Raile said, noting that the dynamic could push Sheehy even farther to the right.

That may have been evident this week, when Sheehy became among the first Republican candidates to release an advertisement about Trump's conviction in the New York "hush money" trial, claiming that Tester has supported the "state-sponsored political persecution" of the former president. 

Adding to the dynamic is the possibility that Montana Republicans may want to guarantee GOP control of the Senate, despite Tester's popularity. According to Raile, exit polling from Daines' 2020 election win over a popular Democrat who served as governor suggested that Montanans supported his bid in part because they didn't want Democratic control of the Senate. And with Tester's seat being a key GOP target this year, that same dynamic could be a motivator at the polls. 

Democrats face steep odds of holding the majority this time. Tester is among two Democrats up for reelection in states that Trump won in 2020. And in another five states considered swing states, Democrats' reelection isn't guaranteed.

Things haven't been completely smooth sailing for Sheehy. The veteran came under fire earlier this year for discrepancies in his story of how he sustained a gunshot wound. And while he and his fellow Republicans have tried to paint Tester as the establishment candidate with deep ties to Washington, Sheehy's own connection to Montana has been called into question. 

The dynamic has been especially relevant when it comes to public lands, a key issue for Montanans. Though Sheehy has expressed his support for public land rights, he's faced some attacks from Democrats for being a wealthy out-of-stater coming in and buying up expensive houses and land.

"Across the political spectrum, people are supportive of public lands, and so that's a political winner, and every candidate talks about it," Raile said. "Some of them have a background that makes that more difficult. But if you're running in Montana and not supporting public lands, that's problematic for your campaign."

Kaia Hubbard

Kaia Hubbard is a politics reporter for CBS News Digital, based in Washington, D.C.

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