Trump Gears Up for Battle to Oust Democrats in States He Won

HELENA, Mont.—Jerry Swick, an Army veteran who currently resides in this mountainous capital city, plans to vote this fall to keep Democratic Sen. Jon Tester in Congress. He just doesn’t know how he would tell that to President Donald Trump, for whom Mr. Swick voted in 2016.

Mr. Trump will host a campaign rally in Big Sky Country Thursday in an effort to corral his supporters behind Matt Rosendale, the Republican state auditor who hopes to quash Mr. Tester’s hopes for a third term.