Yeah, a lot of folks think the USA is untouchable and "it can't happen here", but so many other countries felt the exact same way.
You're fine until one day, you aren't. There's no magical barrier making the USA immune to things other nations have experienced.
Lots and lots of guns available to population is the best safeguard. It's hard to build authoritarian government let alone dictatorship when so much of population is armed.
And there is no way Trump will go against gun ownership rights.