The Obama administration negotiated the release of Army Sgt. Bowe Bergdahl, who had been held captive in Afghanistan for nearly five years, in exchange for five senior Taliban leaders being held in Guantanamo. He was reportedly the last POW being held. The problem is, the law requires the administration to consult with Congress when releasing prisoners from the Guantanamo prison, which the administration did not do. Officials from the executive branch acknowledge that they did not follow the law.
UPDATE: To add another level of controversy, Sgt. Bergdahl was evidently a deserter.