Hours after last Friday's massacre in Aurora, Colo., New York Mayor Michael Bloomberg demanded that the two major parties' presidential candidates explain how they plan to prevent such senseless outbursts of violence. "No matter where you stand on the Second Amendment, no matter where you stand on guns, we have a right to hear from both of them concretely," Bloomberg said in a radio interview. "What are they going to do about guns?" Whether you accept the premise that something must be done about guns, of course, might be influenced by where you stand on the Second Amendment and where...