Obama posted a 40% approval rating (Gallup polls) multiple times in his presidency. Also, IMO, this article really sums up why Trump won.
https://www.google.com/amp/thehill.com/blogs/in-the-know/in-the-know/312322-anthony-bourdain-trump-won-because-people-were-sick-of?amp
He gave a very good interview on this. I detest trump as much as the next guy, but his message obviously rang true for enough people to win the election.
I think some of the support for him we are still seeing is simply people in denial, maybe willing to turn a blind eye because no one likes to be wrong and have their noses rubbed in it. I think that last part explains some of it too, backlash against the backlash, so to speak.
Some of them, of course, are simply on board, fully indoctrinated. Either dyed in the wool repubs, closet, or open, racists, and, yes, some despicable people.
But I think a bigger part is purely ignorance of the reality of it all. A lot of people only follow any of this stuff at election time then defend their decision mostly blindly.