Post Scriptus 10/14/2014 - A reader from the other end of the political spectrum pointed to Snopes in order to substantiate that nope Carville never said that. While that may be true, it might not be necessarily so.
James Carville has had a career being Bill Clinton's top political strategist in the 1992 Presidential campaign (pitted against his future wife Mary Matlin, depicted in the caricature on the back of the
jackass donkey). He also has gained notoriety being the outrageous "Ragin' Cajun" political commentator for CNN and Fox News. Furthermore, Carville and Matlin have acted as themselves on the HBO television "K Street" series(2003) which blended the headlines of the day with improvised acting about lobbying in the District of Calamity.
Thus between Carville's braggadocio and his blending of roles, it is easy to understand why so many people readily accept the Ragin' Cajun's purported quote about truth.
It adds a whole new layer to Carville's quote about truth.