Response bias is not as powerful as one might think. Far less so than simply being wrong with turnout model — which the polls mostly are.
And then there is Michigan and Wisconsin, who do not register by party. There are other sources of party data for those states, but they will always be doubtful.
If I had to point at the one numerical factor in play this year it is that Trumps strength is with young, often first time, voters. Coupled with a historical tendency of the young not voting. How that reconciles is undefined. I would hope Lara Trump’s RNC are out registering voters at construction sites lunch breaks where youngsters work.
I was at a republican hqs yesterday picking up signs
The short time i was there 4 kennedy supporters came in who said they were now voting for Trump
Mind u i live in a small town
For what the above is worth