Michigan polling routnley overstates Democrats by massive margins.
That's just wrong. MI polling understated Obama's margin in 2012 by ~6 points
Sitting presidents are often under-polled. I've noticed this being the case since 2004.
There really is no rhyme or reason to who is under-polled and why. Bill Clinton underperformed his polls in 1996.
Just stating an observation I've made over two decades of following politics and polling.
Nate Silver said the track record on incumbents/challenger outperforming their poll is mixed. It's pretty much a wash. This permeates not just through presidential race but in other races as well.