A week into the general election campaign, the first attack ads of Minnesota's U.S. Senate race are on the air. The Republican National Committee and Republican Senator Rod Grams are running a commercial questioning the credibility of DFL Senate candidate Mark Dayton. Dayton is out with his own ad challenging Grams on the issue of Social Security, although it doesn't rise to the level of a personal attack. In the latest in our series of Ad Watches, Minnesota Public Radio's Laura McCallum reports.