A member of Army Sgt. Bowe Bergdahl’s platoon in Afghanistan said Sunday the former Taliban prisoner deserted his post before being captured and fired back against Obama administration arguments that only Bergdahl knows exactly what happened. “After Bowe Bergdahl purposely and willfully walked away, every single mission was titled toward finding him,” platoon medic Joshua Cornelison told “Fox News Sunday.” “We were there. This isn’t some second- or third-hand account.”