It’s actually not illegal to discriminate based on political views depending on state laws. There is no federal law saying you can’t. Religion, age, sex, race all covered but political affiliation is usually not.
https://www.washingtonpost.com/news/volokh-conspiracy/wp/2016/11/25/can-businesses-refuse-to-serve-or-employ-trump-supporters/?utm_term=.5963f4437618
http://www.nydailynews.com/news/national/california-woman-refuses-sell-home-trump-supporter-article-1.3907232
Most people assume you can’t but in a lot of cases, you can. Oddly enough though it’s usually left refusing right and not the other way around.