Opinion | Why Montana Is Slipping Away From Jon Tester

“This election is about making sure we can have a state that is the same state that we grew up in,” Senator Jon Tester warned a group of Montanans packed into a local Democratic field office in Great Falls one chilly evening last month, just 35 days from Election Day.Ticking through priorities like protecting rural health care and supporting veterans, he noted, “You can’t get all this stuff done with somebody who doesn’t really understand Montana.”Watching Mr.

Tester rally the faithful, it’s hard to tell if he really gets it: Gets how much trouble he’s in politically, how much many voters don’t care where you were born anymore, how much Montana has changed.That last part is painful to contemplate.

The 68-year-old has lived his life here, and made a career of winning elections as a Democrat in a red state by being flat-top-and-tractor-driving authentic.But the state’s changing electorate and America’s polarized politics have his beloved Montana slipping away from him, and he has become this fall’s most closely scrutinized senator — the Democrat in the toughest Senate fight, whose outcome could give Republicans control of the chamber next year.Mr.

Tester’s low-key, folksy manner can be read as either unflappability or resignation.His slight Western drawl carries the trace of a smile, as though he’s chewing over some secret joke.

But every now and then, you catch a flash of edge.He shared with the crowd that, earlier in the day, a reporter told him, “The guys in Washington, D.C., they’ve already figured this out: You’re in deep, deep, deep doo-doo.”“But the bottom line is this,” he went on, with a defiant grin.

“The people in Washington, D.C., don’t know jackshit about Montana.” (Casual cursing is part of his good ol’ boy charm.)“That’s a fact.And we’re gonna show ’em.”Mr.

Tester has withstood the prevailing partisan winds before.He is the only remaining Democrat in statewide office in Montana.

He has h...