I think his framing as a candidate in 2016, and the fact that the relationship that he had between many of his voters was purely transactional at that point (particularily with evangelicals), as much as I didn't like the guy, it made it understandable.
Eight years later, that purely transactional relationship is gone for the most part... whether it was deep inside and just waiting to be tapped, or whether Trump himself changed the nature of his voters, a great deal of his support now will defend just about anything he does or his nature. The ultimate irony is that I grew up hearing many people complain about moral relativism (in the era of Bill Clinton in The White House), yet many choose to practice the same moral relativism as it pertains to Donald Trump.
I just started Tim Alberta's book on the subject with respect to Evangelicals, which has been really insightful so far.