I would have to argue that it had a hold long before that.
I'm not sure how to properly phrase it but didn't the Founding Fathers scribe our Constitution to where there wouldn't be "Mob Rule"??
I think it has always been around but it hit the front lines in Chicago. The movement has been in constant motion since then. Or I just became aware of it around then. Remember the Dems were not the same party they are now coming into the 60's. Towards the end of the 60's changes were in the works. A new breed of cat was coming into play.
I grew up in a lever pulling Dem party family. I had a serious struggle to actually change my views when the light hit me square in the eyes. And I really did not care for those people so how could they possibly be right.