I think a lot of it comes down to the foundational mythology of the US. The whole shining city on a hill, the idea of American exceptionalism, and the reverence for the Constitution are all designed to cultivate the belief that the US is the Platonic ideal of human society, and that nothing better is possible.

So when people see the social contract start to fray, their gut reaction isn’t to question the system itself. Instead, they look for nefarious outside agents who are trying to undermine the perfect society the US is supposed to be. That’s why the narrative of Trump being a Russian puppet was so popular. It’s easier for people to accept that he’s an agent of a hostile nation hellbent on destroying America out of envy, than to see him for what he is: an opportunist who is a direct product of the system unraveling from within.