We do this with relationships. Often we suspend our disbelief about the faults of a person that we care about because we would rather believe our constructed version of them. Oddly, we are also just as willing to create or magnify faults in others because it better fits the narrative about the person that we have already constructed. I have to fight against this tendency (and I do not always win) when dealing with students as my first impression of them can often cloud my ability to take them in as a total person. Sadly, we often see this in abusive relationships--with people unwilling to see the truth about a person out of some faint hope that what they want to believe might actually be true.
This is the only logical reason I can find for people whom I know to be intelligent to still support Trump.