Army Sgt. Bowe Bergdahl walked away from his base in Afghanistan June 30, 2009, and by December of that same year, the president's principal military adviser, then-Chairman of the Joint Chiefs Admiral Mike Mullen, knew those details, according to three of Bergdahl's platoon mates who spoke to Fox News. "I asked him (Mullen) if he knew about Bergdahl and that he deserted and he (Mullen) told me that he knew of the circumstances surrounding his walking off," former Sgt. Matt Vierkant told Fox,"(and) that they were developing leads and following leads, trying to do everything they could to get him...