The last “enemy combatant” being detained in America is incarcerated at the U.S. Naval Consolidated Brig in Charleston, South Carolina—a tan, low-slung building situated amid acres of grassy swampland. The prisoner, known internally as EC#2, is an alleged Al Qaeda sleeper agent named Ali Saleh Kahlah al-Marri. He has been held in isolation in the brig for more than five years, although he has never stood trial or been convicted of any crime. Under rules established by the Bush Administration, suspected terrorists such as Marri were denied the legal protections traditionally afforded by the Constitution. Unless the Obama Administration overhauls the nation’s terrorism policies, Marri—who claims that he is innocent—will likely spend the rest of his life in prison...