And the Republicans are being just as vicious with each other.
Rivals have been spreading dirt about former New York City Mayor Rudolph Giuliani and his extramarital affair with a woman now his wife. And Giuliani and others have spread stories about Romney's flip-flops on key issues, Huckabee's role in the parole of a rapist and Thompson's reliance on a fundraiser with a criminal record.
Watch the full report on "20/20" tonight at 10 p.m. ET. (ABC News)