Bloomberg: “The U.S. Chamber of Commerce’s advertising is outpacing both political parties in close Senate races, adding volume to attack ads — some of which have been questioned by fact-checkers — being aired against Democrats. The nation’s biggest business lobby is second only to Crossroads Grassroots Policy Strategies, a Republican group supporting presumptive party presidential nominee Mitt Romney, in airing campaign ads, according to a Bloomberg review of data provided by New York-based Kantar Media’s CMAG, which tracks advertising.”