Wow.

The upper Midwest is where it breaks down. Several states the same color that voted very differently.

Actually, it doesn't break down. The midwest (outside of Illinois) voted very closely and the different shading is pretty close to the actual vote differences. The correlation is just that, an overall thing with variation ... isn't perfect. But Ohio and Indiana are lighter than Michigan and Wisconsin, which voted very narrowly Democratic. Minnesota was less close, and it's darker. Nevada is just as odd for being lighter than California, given that it's thoroughly blue (presidential vote, governor, legislature). But again, the correlation doesn't have to be a perfect 1 in order to be strong.

I was think Iowa and South Dakota and Kansas looked a lot like Michigan and Wisconsin.

"dummy variable" hahahahaha