Social identity and polarization
It’s not just America, it’s happening throughout the world. Once people are associated with certain political beliefs in the eyes of the beholder, they are lesser human beings. These political beliefs are often described as labels, for example “you’re a leftist, therefore you don’t care about free speech” or “you’re a straight white male, there’s no way you understand the struggles of life” In reality what you believe of a certain topic doesn’t dictate what you believe of another topic, nor do the conditions of your birth matter in your life experiences or your political affiliation.
If someone lives in a trailer and has been dealt a bad hand, they will vote for an option they believe radically changes the system because life hasn’t worked out for them. This could be a factor for someone to vote for right-wing economic policy, it has nothing to do with racism in their mind, and being called a racist dehumanizes this person and ignores their actual struggles in society, further disenfranchising them from other arguments. If this same person votes for a left-wing economic policy, it doesn’t mean they want to take away your culture and have complete control over society, they just feel like the state can help with their problems through welfare programs to improve their quality of life.
In America primarily, people have the idea the conditions of someone’s birth matter in electing officials. They think just because someone is a woman, she will be fit for office, I’ve even seen people who favor left-wing economic policy defend Hillary Clinton based on this physical trait, even though her free market ideology is right-wing. Their arguments of “electing the first woman president” will never hold up when the Republican party decides to run a female candidate, even if they have similar policies, simply because the label “Republican” is attached to this person. How can we as a society make rational decisions if we continue to focus on identity instead of policy? We crated a form of tribalism where you are a threat to the in-group simply based on an issue you care about (even though you might think differently on other issues) or the way you look.