If you think back before that, weren't those the most self-centered and selfish ones?

I remember a situation with a friend of mine from back in my Uni days (not a case of him turning out to be a Trumpist but a case of him having drifted away from his family, rather than "facing it like a man" he just kept deceiving them and living a double life until things inevitably blew up) and looking back from my by then far more mature and adult point of view than when he and I became friends I could spot how he was always the guy who put himself ahead of the rest of the group.

I get the impression that Trumpists are those who are a mix of being the most "what's in it for me" types (to the point of putting the satisfaction of petty and even mean personal psychological wants ahead of other people's actual lives) and useful idiot, and those would have a track record of putting themselves first even in situations were one wouldn't act like that with friends.