I wouldn’t use the word “tunnel-visioned”. That implies focused on something and ignoring the things nearby.
I think it’s more accurate to say “ignorant”. Many, probably most Americans just have no clue about most things outside the USA. You’ve travelled abroad, most Americans have not. The US is such an insular society that people can get away with saying things like “Canadians hate their healthcare” and people actually believe them.
I’ve never thought Trump was smart. He sounds stupid when he talks. He doesn’t seem to have a grasp of even basic things. But, now I’m thinking that somehow as stupid as he sounds, he’s actually even dumber. Like, he’s fooling people like me into thinking he has an IQ of 80 when it’s more like 60. In a way that’s impressive.