Just to be clear, I'd also like to go on record that I've not called anyone out as racists. Though I certainly don't believe it is a " cause and effect" situation, it's undeniable that as southern states very gradually became more Republican, they became less racist. As Horn6721 correctly points out, the switch to Republican domination was a very gradual process, not an instant response to the Democratically-sponsored Civil Rights Act of 1964.
I'd also like to point out that the Civil Rights Act of 1964 had numerous controversial aspects, not the least of which requiring public restaurants and hotels to accomodate miniorities. It was seen by many as an overreach of federal powers. It had opponents that were in no way racists. Barry Goldwater and Ronald Reagan, neither of whom could be credibly termed racist, spoke against it on the grounds that it was an overreach of the national government at the expense of the states and the business owners. Goldwater and Reagan are important political figures whose accomplishments elsewhere make their error in judgement here an inconsequential footnote in their overall record. Here as in an earlier post attacked by Horn6721, I acknowledge that Republican support for the Civil Rights Act of 1964, which while less than unanimous, was crucial to its success. Again, I never called anyone racist. Neither party is racist, though obviously they have and continue to harbor racists. Happily, that represents an ever dwindling portion of the American electorate.