I did this a couple of months ago. I'm better for it.
What has happened is that a sizeable and politically significant number of voters have evolved into racist, misogynistic, transphobic, homophobic, xenophobic, hate- and fear-mongering ignorant assholes. The reasons are varied, but can all be traced to various societal factors. The declining population (as a total percentage) of whites in the U.S., media being driven (by market necessity) by profits instead of journalistic integrity, the internet and waves of false and misleading information that anyone can send out to millions of gullible and uninformed people, the failure of our education system, the fact that the U.S. is rich, bloated, overly stimulated and infected with such false myths as "anyone call pull themselves up by their bootstraps" and "welfare queens" and "illegals are sucking up all of the resources paid for by our hard-earned tax dollars." When you add to that politicians who have absolutely zero integrity, no intentions of ever doing anything "good" for the country or the people at large and are only self-interested (which is, itself, caused by fucked up campaign finance laws) and, as a result, they are willing to tell people anything, no matter how untrue, farfetched or dangerous. You know, things like, "Illegals are taking all of the jobs!" "Democrats are socialists!" "Sandy Hook families are crisis actors!" "Trans women are taking over women's sports and gaining access to women's bathrooms to spy on little girls' pee-pees!" and various other outrageous and stupid shit like that. Whites feel (or believe) they are losing their grip on power and want to hear it's not happening or that there is someone to blame and there are things to do about it. So they vote for the assholes riling them up because it makes them feel good. So, in a word - dopamine. Dopamine is to blame for all of this.