Extreme polarization benefits Trump as there is a roughly 35% hardcore who will vote for him no matter how many he kills on 5th Avenue* and elsewhere. So many on the Right will not consider crossing over and voting Dem, as would occur in less partisan times. But I have to think that many in the middle will vote Biden. How mnay modertes/independents are going to vote for more virus, more deaths, more chaos, more asshole Trump dominating the news for 4 more years.
Also I anticipate that a fair number on the Right will just stay home, too disgusted to vote Trump. Which could be important for close Senate races. I don't see this being talked about. I see the counter-theory that some Trump supporters won't admit supporting him in public but will vote for him in private. But I imagine a fair chunk of GOP backers realize what a disaster Trump has been and will just sit out the election.
* In hindsight, a president talking about how he could get away with murder should have been a warning to us all.