There are a few things that make MI naturally tougher than PA/WI, but the one that gets slept on is just the amount of mid-sized cities the state has. Kalamazoo, Battle Creek, Muskegon, Saginaw, Flint, Lansing. Particularly in WI, there just isn't the same sort of dichotomy.
Obviously he can win, 2016 demonstrated that and close polling shouldn't make anyone complacent.... but even with the issues with the Arab community (people who know better have continually ignored the larger demographics of the state in pursuit of the story, frankly), this state is the toughest of the seven. It always has been.