It's Occam's razor. Before civil rights era southern whites were overwhelmingly Democratic, Now they are overwhelmingly GOP.
Today's GOP is nothing like the GOP of the 1950s and early 60s. Same is true of the Dems. You simply can't wrap yourself in the flag of the former GOP.
that being said, cleary what Biden says was racist dog-whistle. As was the Romney reply full of references of "Angry" and "hate" (as in the proverbial 'angry black man'). Same is true of Romney's constant use of the term 'foreign' to describe Obama.