By putting people in 'groups' and having those who support him also enforce this idea that we're all in separate groups and need to look out for own little group--this is how fascism grows, this is how hitler took over Germany, this is how a new Hitler figure could take over America too... It's not outside the realm of possibility sure Germans in 1900 couldn't forsee the horrors of 1940.

Here's a good video from 1947 explaining the whole thing: https://www.youtube.com/watch?v=23X14HS4gLk