"The Republican's criticism is misleading. It implies that Feingold didn't want to protect the lakes. In fact, it was Feingold who co-sponsored the 2001 measure that enacted the temporary ban. Feingold voted against the 2005 measure because it wasn't substantive enough, he has said."
Feingold did attack Johnson first, which implies he is taking the race seriously and is aware of poll numbers that suggest a close contest. But there is a difference between his attack and Johnson's response. Johnson's ad was a traditional negative attack ad. Third party announcer, eery music and a disingenuous claim. Feingold's ad featured the senator stating a position and contrasting that with a position his opponent has taken.
Was Feingold's accusation, that Ron Johnson supports drilling in the Great Lakes, entirely accurate? Probably not. It would have been entirely accurate if he had said that Johnson refuses to oppose drilling in the Great Lakes.
On a slightly separate topic, you have to wonder how often Ron Johnson actually wears the protective goggles that he sports in every TV ad. Especially ironic is that Johnson is rocking them in an ad in which he makes fun of contrived political ads.