Looking at the PVI, Michigan is going red. At one time 20 years ago, Democrats out numbered Republicans there by quite a lot. Today, it's relative even between Republican and Democratic voters. A classic swing state. One also has to remember the once Democratic bastion of Detroit has had a shrinking population. Detroit had a population of 951,000 in 2000 and today is down to 639,000. That's a lot of Democratic voters to lose.
Gerrymandering very well could be the cause in the house. That's not what I'm talking about. That's not what PVI is all about. What PVI does is takes into account the states voting in presidential, senate, governor and congressional. The overall vote in congressional, not who won each one.
Just because Michigan has an R plus 1 today doesn't mean they're automatically going to vote Republican in every election from now into the future. It doesn't work that way. What it means is Republicans have finally caught up with Democrats in the number of voters in that state. It doesn't grantee who'll they vote for. Any state with a PVI of less than 5 for either party is considered a swing state. Independents can easily overcome the PVI advantage of either party. That happened here in Georgia last year. Republicans outnumber Democrats here by a PVI of 3, but independents voted for Biden by 53-44 margin enabling Biden to win Georgia and overcome the PVI of 3 or the Republican numerical advantage.
If independents had voted more 50-50, Trump would have won Georgia.