Barrett, the Milwaukee mayor, was attacked last year when he intervened in a domestic dispute outside the state fair.
Walker said Wednesday in an interview with The Associated Press that the ad was meant as a metaphor. He says, "It has nothing to do personal with Tom Barrett," and that he thinks "any average voter can understand that."
Democratic Party Chairman Mike Tate says the ad is in bad taste. Barrett says viewers can decide for themselves.
Walker says he was simply reacting to negative ads Barrett had been running against him for weeks.
Do we have a "shitbag" tag yet?