BIG SANDY, Mont. — When you’re a Democratic senator up for re-election in a state President Donald Trump won by 20 points, and the president calls on you to resign, you don’t take the bait — even when he's bearing down on your state to rally against you.

And if you’re Montana Sen. Jon Tester, you may even give him props along the way.

“Donald Trump was straight up. I mean, he told me what he thought of me, and that's cool. I might not like it, but at least he did it to my face,” Tester told VICE News in an interview. “That's what Montanans like. They like people to be square with them.”

In reality, Trump made his confrontation on Twitter, issuing an acerbic tweet after Tester, the top Democrat on the Veterans Affairs Committee, helped sink the president’s nominee for VA secretary by publicizing anonymous complaints about him.

That, however, might change — Trump is hosting a rally in Montana Thursday, where he's expected to rail against Tester in prime time.

Tester wouldn’t answer when asked if he thought Trump’s call for his resignation was appropriate, but he did say he doesn’t regret his role in the VA secretary nomination fight.

“Would I rather he not [send the tweet]? Yeah. But he's president of the United States; he can do what he thinks is right. I did what I thought was right, and I'd do it again,” he said.

That tweet added further pressure to what’s already expected to be a tough re-election fight for the two-term senator. Tester has opposed the president on key legislative priorities and nominees as much if not more than any other vulnerable Democrat up for re-election this year. But he believes Montana voters will give him the benefit of the doubt on his record.

“We'll get backlash no matter what we do,” Tester acknowledged, adding, “I wasn't sent here to be a political operative. I was sent here to be a U.S. senator who represents Montana and Montana's values. And I think with every one of those votes, I can justify every one, I'm from a Montana perspective.”

It’s a line any politician might give to defend their tough votes, but the difference with Tester is that voters seem to believe it. A May Morning Consult poll found Tester was the only red-state Democrat up for re-election with an approval rating over 50 percent — and he’s rated by a handful of nonpartisan election observers as one of the least vulnerable red-state Democrats this fall.

The political platitudes may be more believable from Tester because, more than many senators, voters say he does seem to embody the state he represents. For one thing, Tester’s the only working farmer in the Senate. He still heads home on weekends to plant and plow his organic farm with his wife just outside of Big Sandy, Montana. And he butchers meat on the farm and takes it back to Washington, sometimes in a large suitcase.

Tester has been playing up his Montana roots while attacking his GOP opponent, State Auditor Matt Rosendale, as “Maryland Matt” for moving to the state 16 years ago.

But the senator still has to walk a careful line on Trump, criticizing him only on issues that are a major focus in Montana, like trade and the VA, and even defending him on others. Tester called the discussion about impeaching the president among some Democrats "silly talk" and "way premature," because the special counsel investigation is still going on.

"I don't think what he did is going to be an impeachable offense, if he did anything," he said.

But with the president expected to visit the state to campaign for Tester's opponent, the senator knows he's got a long road ahead to Election Day this fall.

“You’re always running from behind,” he said. “Otherwise you’re going to lose.”

This segment originally aired July 3, 2018, on VICE News Tonight on HBO.