As you may have noticed, I am no fan of Donald Trump. Nonetheless, I think that one reason why so many people succumb to Trump derangement syndrome is the cognitive dissonance. The very idea that Trump could be President can cause them to doubt so many things that, for them, have to be true: that people vote rationally, that government is self-regulating as a result, and that when a government office acquires power, whoever ends up occupying that office can be trusted to use that power in the way they want.
Also, many people refuse to say his name. Are we back in an age in which people believed that names had magic powers?