What was the policy that caused them to reverse?
The black vote was normal in 1932, with FDR getting his democrat 23% from blacks, but then in 1936 they went 71% for FDR, and never looked at republicans again.
I don’t know why, it does put the lie to all these claims of why liberal groups vote liberal though, because as we can see, a group can change historical voting patterns on a dime.
We can all guess it had something to do with FDR’s welfare, but it calls for a much more elaborate explanation than that.