Look at the Whitefish '18 numbers though. A lot of the new residents have arrived since 2016. For example Dave Fern (D) from HD 5, which is all of Whitefish.
2016
Dave Fern 56.7%
Opponent 43.2%
D+13
2018
Dave Fern 69.1%
Opponent 30.9%
D+38
So that's a 25 point swing in 2 years. They are building houses in Whitefish like crazy and the majority of residents moving in are hipsters from Washington and Colorado etc. and they bring their progressive voting patterns with them.
Tester won Senate District 3 (Whitefish and N. Kalispell) in 2018 by 4 points whereas incumbent Keith Regier won it by 13 points in '16. That's a 17 point swing in 2 years.
Interesting indeed. Do you have any insight on Ravalli County, which appears to be second only to Flathead as being the major Republican vote sink in Western Montana?