I would boil it down to one major problem. He is a fucking ignorant idiot.
You usually have to be ignorant to be racist. People who are educated and experienced with other diverse people, may still have the stereotypes that we all grow up with as part of the culture and media, but we are typically able to counter them with many examples of people who contradict those stereotypes. You actually have to work to hold onto them once you have some experience with the world outside your bubble.
Tuberville has never seemed very intelligent. Unfortunately, he fits several stereotypes himself based on his background and geographical location. Stereotypes that I try not to propagate, but again, he fits right in there. Unlike say John Kennedy from Louisiana, who likes to play the "old timey" "folsky" good ol boy, but is actually a Rhodes Scholar, I would imagine that Tuberville is just a meathead that was good at coaching football in a state that loves football, and that propelled him into a position he very much does not belong and is completely unqualified for.
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