Jon Tester, who is leading Rosendale in the polls despite the state's Republican lean. Trump's speech was, like most of his addresses, a remarkable mix of stream-of-consciousness thinking, fact-challenged claims and demagoguery.
Hundreds of people began lining up outside the arena a full eight hours before Trump was scheduled to speak.
Security for the event has prevented any mad scrambles for the best seats in the house, but the arena is expected to be packed when President Trump arrives.
Trump's speech on Thursday night contained a number of genuinely risky lines, lines no president before Trump would even considering uttering among a small group of friends - much less in front of thousands of people. "She gets special treatment under the Justice Department".
Trump also talked tough about upcoming meetings in Europe with members of the North Atlantic Treaty Organisation military alliance and Russian President Vladimir Putin. The reporters then waited for President Trump to come down the stairs to the dignitaries waiting to greet him. And in the middle of the debate, when she proclaims that she's of Indian heritage, because her mother said she has high cheek bones.
His barbs against the media came on a day when newsrooms across the US held a moment of silence in remembrance of five Maryland newspaper staffers who were fatally shot last week by a man who authorities say held a grudge against the publication.
Democratic Sen. Elizabeth Warren of MA. Jon Tester, who as the top Democrat on the Senate Veterans Affairs Committee brought forth a series of allegations against Jackson, who interacted frequently with Trump as White House doctor.
The president also said the IQ of Democratic Rep. Maxine Waters of California, with whom he has clashed many times, is "somewhere in the mid-60s". Trump excoriated Tester for voting against the Republican health care plan, the Trump-back tax cuts, strict immigration laws and Neil Gorsuch, his first pick for the Supreme Court.
Trump tells the rally that Rosendale is a "tough cookie" who will "fight for you". It says, "Welcome to Montana, and thank you President Trump for supporting Jon's legislation to help veterans and first responders, hold the VA accountable, and get rid of waste, fraud and abuse in the federal government".
"Trust me, we'll do just fine", he said.
At a campaign rally in Montana, Mr. Trump took shots at several Democrats, including incumbent Sen.
Tester took out full-page newspaper ads welcoming Trump to Montana on Thursday.
Rosendale said he'll back Trump's agenda, while Tester said he'll support the president when it's in the state's interests and oppose him when it's not.
Trump also mocked President George H.W. Bush's slogan during his rally.
This week, the president interviewed roughly a half dozen potential nominees from a list prepared by conservative lawyers and legal scholars. "A rally in October is probably more meaningful than any rally in July", Johnson said, though he noted that Trump's appearance would certainly draw enthusiasm from supporters he needs to turn up in November. So I sort of feel guilty about this whole thing, ' Trump shared.
And he slammed critics who suggested that he was not prepared for his coming meeting with Putin in Finland, dismissing Putin's background as a head of Russia's intelligence service.
"Fake news. Bad people", he said, later adding that he and Putin "might even end up having a good relationship".