The greatest source of cognitive dissonance for liberals trying to understand Trumpism is that they've spent their whole life training themselves to view the world in terms of nuance, empathy, complexity, and causality, and they're not comfortable accepting that some things actually do lack any redeeming qualities.
It's hard for us to just say "you're wrong, end of story." We reflexively expect the other side to have some sort of valid comeback, some humanizing sob story involving tragic socioeconomic circumstances that magically justifies the mountain of stupidity and cruelty that flows through their brain every day.
Nobody wants to use the phrase "dumb white trash," even if it's exactly what we're all thinking, so instead liberals come up with these patronizing justifications like "Oh they can't help it they're White supremacists, they come from Kentucky! Everyone knows what backwards savages they are!" as if it's physically impossible for people who live in the Deep South to behave like normal human beings and therefore cannot be held accountable for their actions.