Q2 reports that Montana’s four-way Republican U.S. Senate primary is June 5th, and the candidates – along with plenty of outside money – are blanketing the airwaves and mailboxes with last-minute attack ads. The winner of the GOP contest will take on U.S. Sen. Jon Tester in the general election in November. He’s considered one of the more vulnerable Democratic incumbents in the country, based on President Donald Trump’s margin of victory in Montana’s 2016 general election. Trump has already begun targeting Tester via Twitter. State Auditor Matt Rosendale is the presumed GOP front-runner over Russell Fagg, Troy Downing and Al Olszewski– although no independent polling can corroborate that presumption. The open primary, an extraordinary $3 million of outside spending on the race, percentage of voter turnout and the possiblity of Trump fatigue make predicting the outcome even more difficult.