I my lifetime (and I'm pushing 52) they have never had any clout.
They have been the liberal boogey man since their last hurrah somewhere in Indiana, sometime in the 20's.
That was about it for any real power the Klan held (and in the 20s in the midwest they DID have real power). It hung on in some areas for a few years, had a small resurgence during the civil rights era, but now it's just a very small group of very uneducated and very angry and very trashy old men. I guess an individual here and there might still be capable of violence, but as far as any sustained threat to anybody, nah.