I'm not sure about the majority but my dad has this mentality that liberals are the corrupt ones and you're delusional if you think Republicans are corrupt in any way.
Showing him this new from many different sites only results in "the libs are behind this and just trying to discredit the other side." (But an article on a conservative site that can't be found anywhere else is completely legit) There's no reasoning with that type because reasoning isn't there anymore.
On the plus side, I haven't had a great relationship with him my whole life. I've cut him off from my life several times and the only reason I started talking to him again was because he seemed different (from previous issues between us) at his dad's funeral. He has at least followed my stipulations I set if he wants to continue to talk to me.
Sorry to hear about your best friend. Hopefully it's still one of those good relationships 'as long as politics don't come up' kind of thing. But that's a difficult one nowadays.