Three-term incumbent Democratic U.S. Sen. Jon Tester of Montana is facing perhaps his toughest reelection challenge yet.

The FWP study was launched in 2013 as moose strongholds, like the state of Minnesota, were seeing populations of the big, odd-looking ungulates crash.

In the race's final days, Tester's campaign plastered Montana newspapers and airwaves with advertisements amplifying claims from a former park ranger that Sheehy lied about a bullet wound in his arm.

Democrats had a significant cash advantage, and in the race’s final days, Tester’s campaign plastered Montana newspapers and airwaves with advertisements amplifying claims from a former park ...