Before World War II, who did Americans compare people to in situations where "x is as bad as Hitler" would be used today?

by snappingmyfeet
hamiltonkg

You can give this FAQ entry by u/kieslowskifan a read, as well as Before Hitler and the Nazi's, was there another go-to historical "worst person ever"? by u/DavidlikesPeace.

Because of the nature of this question though, someone might have something new to add to the record.