In late 2001, when the Pentagon decided to put detainees at the U.S. military base at Guantanamo Bay, Cuba, the task of setting up a camp and establishing its rules went to Marine Brig. Gen. Michael Lehnert. Lehnert planned to rely on what he learned while running a camp at Guantanamo in the mid-1990s for nearly 19,000 Cubans and Haitians trying to flee to the United States. And he was determined to follow the spirit, if not the letter, of the Geneva Convention, providing decent food, banning extreme interrogation and allowing religious services. He brought in a Muslim chaplain and...