“Really bad scenario. It’s just not a good situation,” said Sen. Joe Manchin (D-W.Va.). Manchin is backing Tester and has tried to stop senator-vs.-senator campaign appearances, even previously endorsing two moderate Republicans.

“I know it’s not a very close relationship,” Manchin added. “I think I’m accurate in that.”

The next two years will be a stress test for the two Montana senators. Their state is one of only five with Senate delegations split between the parties, a modern low. And three of those states, West Virginia, Montana and Ohio, are the fulcrum for next year’s battle for the Senate majority.

They’ve never run against one another, but the Tester-Daines relationship was already strained as they sided against each other in past Montana elections. Now, during a make-or-break race for Tester and Daines’ huge mandate to take back the majority, a palpable chill is setting in.

Daines responded to Tester’s reelection announcement by likening the Democrat to Steve Bullock, the former governor who challenged Daines in 2020 — only to be trounced by double digits. Tester, who spoke to Bullock during his recruitment, deadpanned in an interview that his relationship with Daines “couldn’t be better.”

Asked if Daines took the National Republican Senatorial Committee job specifically to defeat him, Tester replied wryly: “That’s your perspective. And I don’t necessarily think that perspective is wrong.”

Their interplay will demonstrate just how much Washington’s perpetual campaign affects policymaking — and the interests of an entire state. The duo tussled over a Montana judicial pick in December, a potential sign of things to come.

On a personal level, the two men represent the divergent profiles of their Western home: Tester the blunt-speaking, self-described “dirt farmer” versus Daines, a buttoned-up conservative with Trump ties. The tension between them is a reminder, said Sen. John Cornyn (R-Texas), that “none of this stuff’s easy. It’s not for sissies.”

Outwardly, Tester and Daines maintain at least a veneer of civility. They still put out joint press releases, a sign that their offices work together. Yet it’s clear things are strained, judging from clues both past and present.

This week, Montana Republicans are seeking to limit third-party bids with a bill that creates a “top two” jungle primary— albeit only for Tester’s 2024 race. In theory, it would help the GOP head off a spoiler effect that helped Tester win reelection in 2012, when a libertarian siphoned votes from the Republican candidate. But in 2018, Tester surpassed 50 percent against Republican Matt Rosendale, who’s now a House member; the libertarian candidate that year received just under 3 percent.

The Montana bill’s chief sponsor, Rosendale backer and state Sen. Greg Hertz (R), sought to make all races subject to a “top two” system but faced statewide resistance. Hertz said Chuck Denowh, a Montana lobbyist who lists finance work for both Daines and Rosendale on his LinkedIn page, then offered to help. They eventually settled on a bill specific to Tester’s race.

“I mean, how much more obvious can you be?” asked GOP state Sen. Brad Molnar, who voted against the Tester-specific plan. He warned the bill could outrage Libertarians and guessed that the RNC, which has not “had a good idea in 20 years,” was probably behind it.

Hertz, however, said he didn’t talk to Daines or the NRSC about the effort and was unaware if Denowh advocated for it on behalf of any particular client. Denowh did not respond to a request for comment.

“I don’t know if it would help them or hurt [Republicans],” added Hertz. “My main goal is just to make sure that the person who wins the U.S. Senate race in Montana has more than a majority.”

It’s the latest twist in a state where political mischief borders on sport. A mysterious left-leaning group in Montana boosted the Libertarian candidate in 2012 to 6 percent of support, more than Tester’s winning margin. Democrats then fought to remove the Green Party from the ballot in 2018 and 2020, while the GOP helped the Green Party gather signatures in 2020.

Daines and Tester are no exception to the Montana trend. They nearly clashed directly a decade ago, when Daines briefly launched a campaign against Tester during the 2012 cycle. He ultimately decided to seek an open House seat instead, winning easily.

They have now served together for a decade, including in the Senate since Daines’ 2014 win. But Daines grew close to Donald Trump during his presidency, and his son Donald Trump Jr. as well. So when Tester faced reelection in 2018, Daines teamed with the Trumps to stump for GOP challenger Matt Rosendale down the stretch — arguing that “we need to send a different senator” to Washington and urging Trump to come deliver a knockout blow for Rosendale.

Tester won.

Then, in 2020, Tester played at least some role in drafting Bullock, then a former presidential candidate, to take on Daines. Tester said that Bullock made “that decision on his own.” Still, Tester spoke of his hopes that Bullock would run and said his state “needs a senator in Washington that will stand up for Montana, not take a seat because leadership tells them to.”

And Tester knows Senate races: He’s won three and chaired the Democratic Senatorial Campaign Committee in 2016.

“I’m sure Jon Tester has something to do with the race between Governor Bullock and Steve Daines,” said Rep. Ryan Zinke (R-Mont.).

Zinke is among the potential Republican recruits to take on Tester, whose reelection bid Daines greeted with a frosty statement that both he and Bullock “should have ended their political careers on their terms. Instead, they each will have their careers ended by Montana voters.”

Perhaps understating things a bit, Sen. John Thune (R-S.D.), said “there’s some stuff in Montana politics that goes back a while.”

Sen. Jerry Moran (R-Kan.), a former NRSC chair, said he hopes the situation between Tester and Daines “doesn’t become terribly personal.” But “I don’t know how you avoid that.” Moran, who works closely with Tester, said he’s trying to stay out of it.

Other potential Tester challengers include Rosendale, Montana Attorney General Austin Knudsen and veteran Tim Sheehy. As of now though, Tester has no top-tier opponent.

Yet Daines insisted he and Tester “are friends” despite it all.

“He supports about everything the Biden administration has tried to do, and I fought against that: massive spending bills. tax increases, judges. Across the board. So there’s a real clear contrast,” the Republican added in an interview.

Though Democrats have spent a dozen years reading media predictions that this election cycle will be Tester’s last, so far he’s withstood nearly every kind of GOP challenger. This cycle’s intense Republican focus on Montana, however, raises the question of whether Daines’ NRSC chairmanship gives Republicans an edge.

“The people running the NRSC are McConnell and corporate America. We know that,” said Sen. Sherrod Brown (D-Ohio), a fellow endangered incumbent who vowed Tester would prevail. “I don’t think it matters who the figurehead is.”

Ally Mutnick contributed to this report.