That is true, right up to 1964. That's when everything changed. The South was heavily Democrat, but switched to Republican after Johnson passed the CRA. So most of the racists migrated, and continue to this day, to the GOP.

No, it isn't true. The south evolved, as places do. Saying "All the racists moved to the GOP" is a feel-good story the democrats tell themselves:
270towin.com - Historical presidential elections

1976: Jimmy Carter wins the entire south: 270towin.com: Presidential Election of 1976
1992: Bill Clinton wins LA, MO, AR, TN, KY, GA and WV: 270towin.com: Presidential Election of 1992
1996: Bill Clinton wins LA, MO, AR, TN, FL, KY and WV: 270towin.com: Presidential Election of 1996

So were all the racists so mad they decided to wait until the 2000 Presidential election to finally swear off voting democrat?

Or are we maybe willing to entertain that the democrat party is too far left for them to stomach anymore?

I really dislike lazy tropes, and this "all the racists started voting Republican" is one of them. Demonstrably untrue on its face, and further proven false when one looks at who wants racial quotas today.