Michigan he seems to be doing better in +3 to +9, Iowa he isn't (-3 to -10%). The rest is margin of error. And honestly, Biden doesn't inspire the confidence in his potential supporters that Trump does amongst his.
I view this much differently. In 2016 there were enough people who disliked HRC that they were willing to give Trump a chance, or simply not show up to vote (like the very low turnout among African-Americans). Biden has spend literally decades making himself known to this very crucial (to the Dems) voter block. I actually see some enthusiastic support for him in a lot of the east-coast inner city areas.
What’s changed is that the passionate and widespread DISlike of Trump exceeds what was felt for HRC 3.5 years ago. Yes, Trump has passionate supporters (many of whom still want to just poke the establishment in the eye), but he has no more of these supporters than 4 years ago, and he has way more people who are so thoroughly disgusted by him and his administration that they are very likely to show up to vote.
Harbingers of this have played out over the last wave of elections. The 2018 midterms produced the predicted ‘blue tsunami’ with record turnout. Special elections. In deeply red states like Georgia, TX and WV have been way, way closer than they should. More recently WI elected a liberal judge alongside record turnout in the middle of a pandemic.
The passion may not always be
for Biden, but it’s been steadfastly
against Trump. In 2016 he won with approximately the same number of republican votes that Romney and McCain got (that is, those who self-identify with the GOP vote for the candidate regardless, such is how strong party identity is among Republicans). Whereas HRC had substantially low turnout.