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
- Loads of people have already voted meaning Trump actually needs there to be a disproportionately large late swing