Greg Sheridan had a very interesting column in the Weekend Australian dissecting the polls in the face of the unique US voting system. His analysis is based on interviewing a number of respected US pollsters.
For better or for worse, the electoral college system in the US results in a slight gerrymander against the populous states. That's why Clinton received more votes than Trump, but lost in 2016. In that election Trump barely bothered to even campaign in some of the larger states which will fall to the Democrats anyway eg California and New York. So, whilst Clinton polled very well in those states, many of the votes are wasted - 50% + 1 is a win and anything above is wasted.
The analysis suggested that Trump is a chance of winning if he is within 4% of Biden come polling day, not only because of the import of that electoral system but also the fact Trump can inspire voters to come out and vote, whereas Biden lacks any inspirational qualities. The crux will be the debates, assuming how they proceed. Biden is not expected to perform well at all and Trump may close the gap despite his abysmal record in handling this pandemic. The other big unknowns are Biden's running mate, who might be a game changer, and whether the China tensions escalate.
