The polls in 2016 were wrong by 2-3 points nationally and 4-6 in PA and other Midwestern States. Trump needs them to be 2 points more wrongly than in 2016, despite fewer undecided/other party voters. Unlikely, but not implausible. The world needs the miracle to happen 
There are two factors making the leads here more sustainable besides polling firms have largely corrected their education weighting errors:
- Being wrong about a 4-6% margin is much easier to do when there's a higher number of undecided voters, but Biden is already around 50%, so it's not there's nearly as much uncertainty
Yeah, it is what I said. But new errors might arise. Obviously, not necessary in Trump direction. Trump's narrow win, perhaps, is as likely as Biden 12+% landslide. Unlikely, but not implausible.
- Loads of people have already voted meaning Trump actually needs there to be a disproportionately large late swing
If polls are right. If polls are wrong as 2016 + 2%, Trump won't need any swings.
