Friendly on the Senate Floor, Combatants on the Campaign Trail

As the Senate wound down for the summer last week, Senator Steve Daines, Republican of Montana, issued a celebratory news release upon winning approval of a water-rights agreement that had been years in the making.

“DAINES, TESTER LED FORT BELKNAP WATER COMPACT PASSES SENATE,” proclaimed the all-caps headline over the release, in which Mr. Daines shared credit for the long-sought achievement with his home-state Democratic colleague Senator Jon Tester.

Mr. Daines, the head of the National Republican Senatorial Committee, has had other, less laudatory things to say about Mr. Tester recently. Among them: that Mr. Tester did not take seriously enough the national security threat posed by the Chinese spy balloon that passed over Montana this year, and that he needs to be knocked out of the Senate and replaced with someone whose thinking aligns more with Mr. Daines’s.

The campaign committee Mr. Daines leads has been lobbing bombs at Mr. Tester for months.

“I mean, we do have very different and strong views,” Mr. Daines said of Mr. Tester. “You look at virtually every major vote of consequence in the U.S. Senate, Jon has voted one way and I voted the other.”

Mr. Tester and Mr. Daines are the Senate frenemies of the moment. Mr. Tester’s status as a top target for Republicans in 2024 and Mr. Daines’s position as head of the committee charged with unseating him have combined to create an awkward situation where the two Montanans are in a political fight to the finish, even as they cooperate on state issues.

The Montana race is one of a handful of contests likely to be decisive in determining who will control the Senate, currently held by Democrats by a 51-49 margin, in 2025. The seats held by Mr. Tester, Senator Joe Manchin III of West Virginia and Senator Sherrod Brown of Ohio are all in the sights of Republicans since President Donald J. Trump convincingly carried the three states in 2020. Posting a home-field win would put Mr. Daines well on the way to achieving his party’s goal of taking the Senate after Republicans underperformed in the last two election cycles.

It has made for plenty of dissonance in an otherwise professional, even cordial, relationship.

The dynamic was on full display last week as the two senators joined forces to successfully add a provision to a Pentagon policy bill granting approval of a Montana water-rights compact that has been the subject of decades of difficult negotiations between Native American tribal interests, farmers, state and federal agencies and others. With the legislation heading to a vote, the two could be seen amicably consulting on the Senate floor while the Senate Republican Conference was readying a podcast in which Mr. Daines took a shot at Mr. Tester over the spy balloon.

Mr. Tester appeared unfazed.

“You’ve got to compartmentalize,” he said about the unusual state of affairs. (That is not to say there is no competition between the two even on team efforts; Mr. Tester put his own name first on his version of the joint news release with Mr. Daines about the water agreement.)

Senators have traditionally been reluctant to campaign too aggressively against their home-state colleagues on the theory that they might need them in the future if they win. Also, it was once considered a violation of the clubby Senate code to go too hard against a fellow incumbent.

It was practically a national scandal in 2004 when Senator Bill Frist, a Tennessee Republican who was the majority leader, traveled to South Dakota to campaign against his Democratic counterpart Tom Daschle. That kind of thing just wasn’t done.

But given the intensifying partisanship on Capitol Hill and with control of the Senate at stake, the old rules do not apply. And Mr. Daines is not just calling for Mr. Tester’s defeat — he recruited a top challenger and is responsible for a campaign operation that will devote millions of dollars and untold hours of political plotting to achieving that outcome.

“Both of them are focused to win, so it is natural it would create some division,” said Senator Gary Peters of Michigan, who as head of the Democratic Senatorial Campaign Committee will be trying to help Mr. Tester come out on top.

Mr. Tester has won three tough Senate races, beginning with knocking off a Republican incumbent in 2006, and now seeks a fourth term. Though Montana has shifted to the right, he has shown an ability to build winning coalitions and connect with constituents, portraying himself as a down-to-earth Montanan with a flattop, a working farm and a common-sense approach to Washington. Not to mention three missing fingers from an accident in his youth.

“I’m pretty different from most people who end up in the U.S. Senate,” Mr. Tester said in a typical fund-raising appeal this year. “I’m just a dirt farmer trying to do what’s right for the people in my state and across the country.”

Despite the political conflict, there are good reasons for the two to cooperate when it comes to doing Senate — and Montana — business. Mr. Daines can certainly use Mr. Tester’s help when it comes to getting things through the Democratic-controlled chamber. And it doesn’t hurt Mr. Tester to be able to claim some big bipartisan wins alongside a man determined to oust him.

The two have never gone head-to-head, though Mr. Daines briefly entered the 2012 Senate race against Mr. Tester before turning his attention to the House and winning a seat there; he jumped to the Senate in 2014. And Mr. Tester backed Gov. Steve Bullock in his race against Mr. Daines in 2020, a race Mr. Daines won surprisingly easily.

Mr. Daines said that he considered Mr. Tester a friend and that he had not sought the chairmanship of the campaign committee to take on Mr. Tester. It was simply coincidence, he said, that he got the job in an election cycle when a fellow Montanan would be on the ballot. He likened the situation to a sporting event between longtime rival teams.

“When the game’s over, you say ‘good game,’ and you maintain a relationship and friendship. That needs to be true in the political arena,” he said, adding, “You can still disagree without compromising a friendship.”

As for Mr. Tester, he brushes off Mr. Daines’s not-so-friendly fire.

“It’s fine,” he said. “I’m still going to win.”