Defense Secretary Chuck Hagel said Thursday the U.S. intelligence community believes the Syrian regime used the chemical weapon sarin, a revelation that immediately raised the question of whether a "red line" had been crossed in the country's civil war. Hagel confirmed the intelligence assessment, which was detailed in a letter to select members of Congress, while speaking to reporters on a visit to Abu Dhabi. The administration swiftly released those letters, which said U.S. intelligence determined with varying degrees of confidence that "the Syrian regime has used chemical weapons on a small scale in Syria, specifically the chemical agent sarin."...