This is why we have the second amendment. And the constitution as the thing to which office-holders swear allegiance to rather than to "the party" or "the president".
It's make-believe, but I guess it makes Americans feel a little special to know that if you elected some dictator you would have a chance to stop them. Your political rulers know far and well that civil war is the last thing anybody wants. Your judicial and political system in place should, before any Hitler came to power, stop them and prevent coup d'état from happening.
It's worrying that we, people living in highly progressive and democratic societies, would have to fear a dictator suddenly coming to power and having to protect ourselves against it. Why anyone would follow such psychopaths and throw away democratic society with free will? But I admit, humans are highly illogical and emotional creatures, that are deep down still driven by the primal urges that are the same as they were thousands of years ago. Just because we dress in fancy suits and dresses doesn't mean we aren't capable of what the Nazis did less than hundred years ago but I'm hopeful that we as species are still slowly progressing.