Instead of asking what we can do to avert a such a slide, maybe it's better to first ask a Red Team style question (http://en.wikipedia.org/wiki/Red_team):
" If you had the means and motivation to turn the US into a dictatorship, how would you go about doing it? "
I'm keen to hear HN's thoughts (obviously not because I have such means nor motivation!). Rather, if the US was to descend into dictatorship it could quite possibly come from a strategy that many have not even considered. Being keenly aware of the ways in which the US could become a dictatorship, may better prepare us to prevent such a horror from happening.