It's a joke about the "party switch"/ "Southern Strategy" narrative. FDR was a liberal president that Democrats love, but he came from the 30's/40's, before the supposed realignment in the 60's. According to the narrative, Democrats were a racist party until the 60's and Republicans became a racist party after that.

It's a joke about the "party switch"/ "Southern Strategy" narrative. FDR was a liberal president that Democrats love from the 30's/40's, a time when Democrats were supposed to be racist, since he was before the supposed realignment in the 60's.