I just responded to someone on Facebook who said that we can't hold the Democrat's past racism against them because all the racists left that party in the 1960s and became Republicans. Here was my answer, for your further research:

The 'major switch' claim isn't true. I went through and cataloged every single US representative, and every single US senator, and every governor, from about 1950 and tracked which ones switched parties through about the mid 1970s, and how many. Almost every Democrat who was a Democrat remained a Democrat their entire careers, and vice versa. Out of the more than a thousand politicians, only about 50 switched.

This info is public knowledge to anyone who wants to do the work to test the hypothesis. I would suggest starting with the people who signed the Southern Manifesto, noting their party, and then cataloging which of THEM and how many switched. (The SM being the most visible subset; if the hypothesis does not stand with the SM, its not likely to stand with the whole set.)

Some other explanation must be the case, because the POLITICIANS didn't switch.