A store calling itself Fearless Distributing opened early last year on an out-of-the-way street in Milwaukee's Riverwest neighborhood, offering designer clothes, athletic shoes, jewelry and drug paraphernalia. Those working behind the counter, however, weren't interested in selling anything. They were undercover agents from the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives running a storefront sting aimed at busting criminal operations in the city by purchasing drugs and guns from felons. But the effort to date has not snared any major dealers or taken down a gang. Instead, it resulted in a string of mistakes and failures, including an ATF...