I can't speak to the Jewish totals, but I can for American blacks. First, it depends on where it happens. If the GOP can scrape off a mere 10% more of the black vote in NY, FLA, and CA, the RATS are toast.
Unfortunately, we have several people here who will go apoplectic when the GOP goes after black voters.
If a black votes for a Republican, it's because the GOP was "pandering," you see.