Why is Montana so swingy and further left than surrounding states?
DEMs generally can perform very well in the Cities, as well as ancestral DEM presence in former mining communities.
Resorts and tourism are strong in Western MT.
Eastern MT is what really drags the DEMs down, other than in Native Land.
I would look at the '08 PRES map as a building block for what the 2020 map will likely resemble, with greater Biden strength in some of the Cities and worse performance in the rural Eastern portion of the State.