Hillary Clinton’s social media manager has a blunt message for the National Rifle Association: “F*** off.” Chris W. Cox, the executive director of the National Rifle Association Institute for Legislative Action, penned an editorial on Monday for USA Today. Mrs. Clinton’s social media guru, Emmy Bengtson, soon responded with profanity to his “Opposing View” piece titled, “Guns laws don’t deter terrorist.” “Radical Islamic terrorists are not deterred by gun control laws. The San Bernardino terrorist attack wasn’t stopped by California’s so-called ‘assault weapons’ ban,” Mr. Cox wrote. “The gun ban in Brussels didn’t prevent the terrorist attack there. And France’s...