WASHINGTON - Christmas 2003 became a season of terror after the federal government raised the terror alert level from yellow to orange, grimly citing credible intelligence of another assault on the United States. "These credible sources," announced then-Secretary of Homeland Security Tom Ridge, "suggest the possibility of attacks against the homeland around the holiday season and beyond." For weeks, America was on edge as security operations went into high gear. Almost 30 international flights were canceled, inconveniencing passengers flying Air France, British Air, Continental and Aero Mexico. But senior U.S. officials now tell NBC News that the key piece of...