Nearly six years ago, President George W. Bush declared Ali Saleh Kahlah al-Marri an enemy combatant and had him swept out of federal court and into a U.S. Navy brig so he could be interrogated without the legal protections afforded by the criminal justice system. Bush said the Qatari national, arrested as a material witness in Illinois in December 2001, possessed critical intelligence that "would aid U.S. efforts to prevent attacks by al-Qaeda on the United States." In an agreement Marri entered Thursday in Peoria, Ill., he pleaded guilty to conspiracy to provide material support to al-Qaeda and admitted to...