Trust me, there is no republican trend going on in MI. Some of the old republican strongholds are solidly Democrat, and those. along with the old Democrat areas win the election for the Dems. We have also had a loss of population, and like any neighborhood going downhill, the more wealthy are able and willing to move away leaving the poor behind. The poor vote Democrat. The only way a republican will win MI these days is if there is a really poor Dem on the ticket.
The best example is Kalamazoo where I am originally from. Used to be a hands down win for republicans. Today, it is solidly Democrat, and every one of my formerly republican family members vote straight Dem today. It is also the home of liberal activist billionaire Jon Stryker whose company makes much of the medical equipment used on you when you go to the doctor.
I would have to say you are wrong. A few years back you would have not think MI would be a toss-up to lean Demorcatic state, but now it is.