WASHINGTON — For the most part, President Donald Trump's campaign to oust red-state Democratic senators in November is just standard-issue partisan politics. But when it comes to Montana Sen. Jon Tester, the fight is personal.

Last week, Trump called on the second-term Democrat, already facing a tough re-election race, to resign. "I know things about the senator" that would cost the incumbent his home-state support, Trump said cryptically.

A few days later, Marc Short, the White House's lobbyist on Capitol Hill, told a Montana radio station that the president was making plans to personally campaign against Tester. And at an NRA event in Dallas on Friday, Trump called Tester's handling of Ronny Jackson's nomination to head the Department of Veterans Affairs "a disgrace."

The top Democrat on the Senate Veterans Affairs Committee turned himself into a prime target for Trump last month by voicing allegations that Ronny Jackson, Trump's pick to head the VA, had overprescribed medications and been intoxicated on the job during his time as the president's White House doctor.

Jackson denied the charges, but Senate Republicans had already postponed his confirmation hearing, and he eventually withdrew from consideration.

The Jackson nomination is over — but Trump's push to oust a man who helped torpedo that bid may be just beginning.

Now the question is whether Montana voters will reward Tester for standing up for veterans or punish him for bucking a president who won Montana by 20 points in 2016 and remains popular there.

"Jon Tester has been relentless in his work to bring tough accountability to the VA," Tester campaign spokesman Chris Meagher said. "Veterans across Montana want Tester to keep working to fix the VA so they get the better health care they were promised and earned. And that includes asking tough questions."

This isn't exactly how Tester had planned to approach the delicate balance of showing he can work with Trump when he needs to and hold the president's feet to the fire when he has to.

His first ad of the cycle, launched in March, featured him looking into a camera and telling voters just how much he and the president agree — particularly when it comes to veterans' issues.

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"Washington's a mess," he said. "But that's not stopping me from getting bills to help Montana signed into law by President Trump." The list: 13 bills, including eight designed to improve the Veterans Administration.

Tester's tack is one that has emerged as a theme among Democrats in deep-red states this election cycle. Democratic Sens. Joe Donelly of Indiana, Heidi Heitkamp of North Dakota, Claire McCaskill of Missouri and Joe Manchin of West Virginia are all touting both their support of, and independence from, a president who is a force in American politics unlike any other in recent memory.

"In red states, we'll see Democratic senators walking the tightrope for their political lives," said veteran GOP strategist Reed Galen. "Fall to one side, your base voters will abandon you. Fall to the other, your angry opponents will devour you."

While some of his fellow vulnerable Democrats have avoided drawing attention to issues where they part ways with the president, Tester has taken some of the boldest risks in challenging him.

Still, despite the risks, the Jackson fight could pay political dividends in Tester's home state. Many veterans groups and Republicans were concerned the president's nominee hadn't had experience managing an institution nearly as large and troubled as the VA — an issue with particular resonance in Montana, which ranks among the top states in the country in veterans per capita.

The senator has to hope most voting veterans have the same reaction as Montana resident Andrew Person, who served in Iraq and Afghanistan: "Congress has a critical role here in making sure whoever is nominated to lead the VA is ready to go, and Tester was doing the right thing," he recently told the Missoula Current.

Of course, the Jackson episode may have been Tester's most high-profile split with Trump — but it was far from his first. He also voted to shut down the government last year as he held out — successfully — for a budget that would provide more funds for Medicaid and community health centers.

He voted against confirming Mike Pompeo, first for CIA director and then for secretary of state. And he opposed the confirmation of Supreme Court Justice Neil Gorsuch, along with most of the major elements of Trump's domestic agenda, including the Obamacare repeal and tax cuts.

In fact, Tester has voted 37.1 percent of the time with Trump's legislation and nominations, according to FiveThirtyEight.com — a far cry from the 85.6 percent score the website says would be the more expected outcome for someone in his political position, given Trump's 20-point victory in Montana in 2016.

Republicans say the latest spotlight on Tester will draw inconvenient attention to that gap.

"This is who Jon Tester's always been," said Calvin Moore, a spokesman for the National Republican Senatorial Committee, which just launched a digital ad in Montana featuring Trump saying "what Jon Tester did to (Jackson) is "a disgrace."

"He has largely relied on coasting through to re-election on the hope that nobody back home looks in depth at what he does in Washington," said Moore.

But despite Tester's Trump feud, there are signs he may be in better shape than some of the other Democrats in a similar situation this year.

A Morning Consult poll released last week suggested that 54 percent of Montanans approve of the job Tester's doing, compared to 34 percent who do not. And in an era in which voters in Republican states are much more likely to say incumbent Democratic senators should be replaced rather than re-elected, Tester is even on that question, at 43 percent on each side of the divide.

Furthermore, Republicans are still sorting out who will challenge him. Their primary, featuring a field of five, won't be settled until June 5. State Auditor Matt Rosendale, who previously ran statewide for Montana's lone House seat, is Washington's leading bet to emerge as the nominee. He has backing from the conservative Club for Growth, one of the best-funded outside groups in politics.

Though Rosendale holds office now, was once majority leader of the state Senate and has lived in the state for more than a decade, Tester and his allies are painting him as a carpet-bagger. His thick Maryland accent leads him to pronounce "Montana" differently than locals, a variation highlighted in a digital ad the Montana Democratic Party put together.

Tester's campaign calls him "Maryland Matt Rosendale" and accuses him of favoring developers at the expense of the public interest.

Whoever the GOP candidate is, Republicans say Tester's ability to tie himself to Trump on policy has been crippled by his fight with the president over Jackson.

"That entire message is gone for him," Moore said.

Tester's political fortunes depend both on whether Montana's midterm voters agree — and how much it matters to them.