I honestly don't think he's winning Michigan. It's going to be decided by three counties - Macomb (affluent Detroit suburb), Kent (Grand Rapids, very religious but Whitmer is from there), and Saginaw (Saginaw, Bay City, Midland) which flipped to Trump. Here is a link to the top 15 counties voting in '16. I don't really see any other counties flipping, Not counting the rogue UP blue county, no chance the blue counties flip. They are strong union counties or big colleges.
https://www.mlive.com/news/2016/11/how_michigans_15_most_populous.html
If you can get a feel for those three, theres your bet. Kent is least likely to flip, Saginaw probably does, especially if the economy stays in the dumps.