I don't have anything insightful to add that hasn't already said, but, one of my favorite #analytical takes was that NH, a state where people attributed all of Trump's 2016 success to opioid epidemic and which he immediately disparaged as a 
drug infested den as soon as he got into office, was maybe going to swing towards him in a race where most of the fundamentals were running against him.
Bernie Sanders might have depressed Democrat turnout or caused a lot of defections in 2016.
I also don't think "insulting" states has much of an impact. Trump said "how stupid are the people of Iowa?" but won it twice. Sinema called Arizona "the meth lab of democracy" and still won.
Yes. It seems to me that certainly the most important thing was Bernie Sanders getting write-in votes or Sanders fans abstaining in 2016; all of this transferred to Biden in 2020. You can see this particularly in Vermont.
Also there are a lot of wealthy towns, e.g. southwest Connecticut, Boston suburbs like Dover - which were in fact very strong for Romney. Some of them swung nearly as much 2016-2020 as 2012-2016.
