Situation: There are two political opponents running for the same position. In politician #1's commercial, he attacks #2 by pointing out flaws in his campaign or history. #2's attack is more clever. He "takes the high road" by saying that he'd never stoop so low as to attack his opponent, while this itself is an attack as it implies his opponent is beneath him, since he has gone so low as to directly attack him.
What's this type of attack called?