Rachel Maddow did a very powerful and important segment about the long, sordid history of anti-immigration hysteria in this country, going back to the know-nothings of the mid-1800s and all the way to the modern day. She correctly notes that Trump is just the latest iteration of American nativism and xenophobia.
And all of this goes back to tribalism and the psychology of the right-wing mindset, which is hyper-reactive to perceived threats from the outside, threats to our collective identity and to the purity of our bloodlines. That’s why Trump is so wildly popular among white supremacists, because his policies dovetail perfectly with their vastly exaggerated perceptions of threats to the white tribe. Watch this whole thing, it’s important.