This video edition of "Steve Schmidt's The Warning" gives an excellent accessible explanation of Trump's continued appeal. He calls it 'The Politics of F*ck You.' He sees a vast swath of Americans having real grievance over the economy and the opioid epidemic and much else. They basically lost faith in all establishment institutions. Trump exploited this, while the establishment just called anyone listening to him stupid. That worked poorly for the establishment. The economy is better now, but folks really don't get that because the RW media doesn't say so. Sure, more people have good jobs than ever, but they credit themselves for that, not Biden....
BTW, Schmidt points out, Trump now looks to ride this thing to a full fascist dictatorship. And he seems to be succeeding.
https://www.youtube.com/watch?v=LTfdmwPZXwM