[Harmless Teddy Bear]

They may be over-weighting Republicans in that sample.

No, they are not.

That was 2012

[Alberta's Child]

That map doesn't tell me anything. The most heavily populated counties in Michigan are blue.

Here's a similar map of Nevada from 2012:

Obama got 56% of the vote in one county and less than 51% in another county. He lost all the rest, most of them by margins of more than 18 points.

He won the state by more than six points overall.

[Dave W]

The number of red/blue counties are irrelevant to the mix of dems and republicans. We all know the rural counties are red and the urban counties are blue.

Hardly anyone lives in the rural counties. More people live in urban counties, which means there are more voters in urban counties. Which means, especially in Michigan, there are a lot more democrats than republicans. Two or three blue counties can out vote 50 red counties.