One of the year’s top Senate races is set in Montana after Democratic Sen. Jon Tester and Republican entrepreneur Tim Sheehy won their primaries Tuesday, NBC News projects.

The race is among a small handful that could be a tipping point for partisan control of the chamber.

Montana — along with Ohio, where Sen. Sherrod Brown is pushing against similar headwinds in his own bid for a fourth term — is one of the GOP’s top opportunities to unseat a vulnerable Democrat. Former President Donald Trump twice won both states by wide margins.

Sheehy, a former Navy SEAL backed by Trump and aggressive investments from national Republicans, will test Tester’s long-established crossover appeal in Big Sky Country.

“I’m not going to downplay it — it’s certainly going to be a difficult race,” said Alex Bruesewitz, a GOP consultant aligned with Trump and Sheehy. “It’s not a cakewalk by any means.”

A Tester loss could cost Democrats their one-seat majority in the Senate, with Republicans likely to gain a seat in deep-red West Virginia, where Democratic-turned-independent Sen. Joe Manchin is not seeking re-election. Already, Montana voters are being deluged with political ads.

Through Tuesday’s primary, Democrats and Republicans had already spent more than $36 million combined on advertising, according to AdImpact, an ad-tracking firm. Another $124 million is budgeted through the general election: $63 million for the GOP and $61 million for Democrats.

“Tim Sheehy is a strong conservative, an American hero and a successful businessman who will bring an outsider’s perspective to a broken Washington,” the chairman of the National Republican Senatorial Committee, Sen. Steve Daines of Montana, said in a statement. “The clearest path to a Republican Senate majority runs through Montana. Tim Sheehy will deliver a Senate majority for President Trump, Jon Tester wants to deliver a Senate majority for Joe Biden. That is the choice in this election. President Trump is counting on Montana to elect Tim Sheehy.”

Tester and Sheehy have been circling each other for months, as neither candidate had to break much of a sweat to win his primary. Trump’s endorsement — and early support from the NRSC — chased Rep. Matt Rosendale, the GOP’s nominee against Tester in 2018, from the primary less than a week after he launched his campaign.

Each candidate is attempting to frame the other as a phony.

Sheehy and the GOP present Tester, 67, as a creature of Washington who pledged to change the culture but became one of the Senate’s top recipients of campaign cash from lobbyists.

“The guy is the epitome of the swamp,” Bruesewitz said of Tester. “He’s no longer the man he was when he originally went to Washington.”

Tester and the Democrats play up the incumbent’s Montana dirt farm roots while emphasizing that Sheehy, 38, is a relative newcomer who grew up in Minnesota.

“It’s going to be a competitive race, I don’t think anybody disagrees with that,” said Justin Barasky, a Democratic strategist who works on Senate races but is not involved in the Montana contest. “But the contrast couldn’t be more clear.”

Democrats are expected to focus heavily on how Sheehy has admitted to lying about the circumstances of a gunshot wound. In one telling, Sheehy has said he was wounded in combat while serving in Afghanistan. In another version, first reported by The Washington Post, he told a park ranger that he accidentally shot himself while visiting a national park in Montana. Sheehy told the Post that the park account was a lie, meant to ward off an investigation into a combat injury he said he never reported to his superiors when it happened in 2012.

“Who lies about how he was shot?” Barasky asked, referring to Sheehy. “He’s kind of his own worst enemy. And ultimately, it’ll be one side of the coin to how Sen. Tester emerges victorious. The other side obviously being, you know, that Jon embodies his state like nobody else.”

Tester allies also have pushed stories about Sheehy’s aerial firefighting company and a cattle ranch that he and his business partners operate in prime elk country. The ranch does not allow public hunting on its grounds — a polarizing issue in a state that traces its origins to federal homesteading programs and where some advocates believe all land belongs to the public.

After Sheehy’s primary victory was called Tuesday, the Democratic Senatorial Campaign Committee released a minute-long digital ad, titled “Shady Sheehy,” that references the gunshot wound and other stories that have scrutinized the candidate’s past.

“Sheehy represents everything Montanans hate about rich out-of-staters, and after he’s been caught lying about every part of his life, he’s shown Montana voters why they can’t trust him to look out for anyone but himself in the Senate,” DSCC spokesperson Amanda Sherman Baity said in a statement.

Trump’s conviction last week on 34 felony counts in a New York trial over a hush money payment to an adult film actor could emerge as a new tension point as the race officially shifts to the general election.

Tester barely reacted to the jury’s verdict, with a spokesperson telling local media that voters would decide Trump’s fate in November. Sheehy’s campaign, meanwhile, cut a TV ad accusing Tester of participating in a political persecution of a former president who won Montana by more than 15 percentage points in 2020. The 30-second spot also features a clip from a Tester appearance on MSNBC’s “Morning Joe” in 2019, when the senator, speaking figuratively, spoke of the need to stand up to Trump and “punch him in the face” when he says offensive things.

“They want to throw Trump in jail, trying to rob Americans of their choice in the election” a narrator says in the ad. “And Jon Tester is standing right by their side.”

This article was originally published on NBCNews.com