A blog post by Ilya Somin in Volokh Conspiracy reminded me of a former German named Pinkie.

One of the commenters (Joe Horton): It seems to me that the Nazis got power not so much by getting votes (which they were able to do in a number of ways) so much as by killing, or at least beating the cookies out of people and families of people who disagreed with them. Once legitimate law enforcers were cowed by the apparent burgeoning Nazis, they, too, came under the spell. This is all pretty well described in the recent book, In the Garden of Beasts: Love, Terror, and an American Family in Hitler's Berlin, which details the ambassadorship of William Dodd to Germany in the 30’s. It makes fascinating, if chilling reading.
Another (SteveMG): Sydney Hook, in Out of Step: An Unquiet Life in the 20th Century, says he was immediately shocked and frightened at seeing Hitler speak. His ability to mesmerize the audience, his outright racial appeal, his open promotion of violence, his appeals to “blood”, it was all there.

Erik H adds at the end a book which also looks interesting,