There are quite a few of my acquaintances who smell the odor to which Lupin refers. Most of them either had families in the holocaust or were second generation Americans who had a family history of authoritarian governments. Tellingly, about half of them have emigrated and a lot of the others are seriously considering it.
Other people I know think the rest of us are paranoid but when you confront them with things like, "the vice-president shot someone in the head and the victim had to apologise," or, "what about those detention camps they're building outside of town?" they just let their eyes slide off and look in a corner. That expression they get on their face scares me more than any right wing nut ever could.
Would the military ever come into play? There are some crazy commanders, and I personally know a bunch of very crazy enlistees, but I think that the military would be more likely to split and fight among themselves than the general populace would. Just guessing though.