Democrats were never Republicans or vice versa. Prior to 1964 both parties had a diverse balance of Bigots. Democrats having a large contingent of racist southern Dixiecrats. Republicans had also long been the party of fascists and Nazi sympathizers. What happened post 1964 was not a party or ideological switch per se. Democrats just ditched the bigots courting a much bigger potential voting block. Republicans having lost the chance to court the same voting block instead courted the bigots fleeing the Democratic Party. It was a concentration of bigots. Not a change of ideology.