Why is Southwest Wisconsin bluer than other regions in the state?

[Mr. Illini]

Madison bleed over?

Yep, these areas were ancestrally R until Madison became a huge force in the region. The area (I'm thinking places like Onalaska) is great for tourism, which also brings in a Vermont-like shift in the environment. 

But, the areas across the border in Iowa and Illinois vote similarly.

I attribute it to higher shares of Swedish population and a more influential manufacturing sector.