It's not whites voting more Republican, it's a rural-urban divide. Some states were really resistant to this change until the election of Obama, while the states that Obama expanded the map with have been urbanizing and building suburbs close to the city. Pennsylvania is shifting as Philadelphia and Pittsburgh lose population, and I suspect Michigan and Wisconsin will see a similar trend in the future as well.
It's not really an acceptable long term fix though, because pretty much most of the population growth in the US is happening in southern urban cities like Charlotte, Atlanta, Austin, and Houston. I suspect that the future map in 10-20 years looks something like this, in which Democrats can realistically challenge Republicans for the entire South and Republicans can sweep the Midwest:
