The Romney advertisement that's completely unauthorized.
I know some will complain about the political left voting in a Republican Primary? But would you prefer they vote for Ron Paul? Eeeek!
Seriously, I doubt the cross-over voting will have that much of an effect. If it does, it's more likely to help John McCain. There are just not that many "tactical" voters to have an impact. If there were, Jesse Jackson would've won Wisconsin in 1988.
Ht: Folkbum