That’s a good point about the difference between pre-election polls and final results, but I don’t know if you can make that correction for 2020. Presumably, people who voted for Trump in 2016 and plan to vote for him again are not shy about it anymore. They would have no reason to lie in the current polls. But Wisconsin does seem to be leaning toward Trump right now. Some of the other battleground states are not.
A lot of Democrats are really worried about party unity right now, but I have a feeling they’ll be plenty unified in November. The two oldest Supreme Court justices by far are both Democrats, and no Democrat wants to roll the dice on the chances of letting Trump swing the Court to a 7–2 conservative majority. They’ll all vote for the Democratic nominee, even the Bernie Bros.