Do stupid people know they're stupid? And do stupid people recognize other stupid people when they see them?

I ask this because every Trump supporter on my FB friend’s list (only about 5 people) is stupid. I mean, really stupid. We’re friends for whatever reason, HS or something, so we have fun, but we never have deep conversations like I can have with some.
But when it comes to Trump it’s insane. Can’t they look around and see that the only people who support Trump are stupid people, and perhaps question themselves over that? Or do they not know they are stupid, and do they not recognize stupid people when they interact with them?