In order to see it, you must recognize the ways in which he fooled you. People would generally rather be fooled again than face the thought that they were fooled at some point in the past. And the more that they have been fooled, the stronger this bias is.

Trump is an absolute genius at fooling people in small ways, then over time ratcheting up the cognitive dissonance until he fools them in big ways. See https://specialto.thebulwark.com/ for a detailed explanation of how he did this with one of the many people that he has turned into puppets.