The democrats attack the one they are most afraid of. Look at the liberal press that the democrats have in their back pocket. Who ever leads in the polls for the GOP is the one they attack. It has been a really effective tactic.
It has been repeated with every front runner. Their biggest tactic is accusing someone of being dumb. Obama can't talk without notes on his TelePrompTer. Have you noticed the overwhelming lack of criticism of Obama on every major network like ABC, NBC, CBS, CNN and all the rest. Whoever controls the media controls the morons who can't think for them self.
No where was this more evident than with Cain. One accuser filed a sexual harassment complaint with her new boss after she left being employed by Cain. The other lives in the same building with one of Obama's right hand man.