Well, they hid the fact Ashley was a Klansman in the movie.
By 1940, the Klan had dissolved into small cliques in places like West Virginia, where Robert Byrd was a member. Which is why John Kennedys victory in the 1960 West Virginia primary was taken as proof that a Catholic could win nationally. Of course, at that time, it was known how much money Joe Kennedy had spread around the state.