Nobody votes against somebody they were planning to vote for because somebody they don't like suddenly endorses them.
Well hypothetically it's possible
Imagin if some GOP SuperPC made this ad and spent a million to air it nonstop in ATL:
Hi, I'm David Duke, former Grand Wizard of the KKK. In this election I support Michelle Nunn, because I personally believe she has the guts to resegregate out schools and remove the Jewish influence from our banks. Vote Michelle Nunn - for a racially pure Georgia!
That's a pretty extreme example and probably out of the bounds of what Griff was talking about.
Thanks for pointing this out!