As President Donald Trump was heading to Singapore for a historic summit with North Korea's leader, a State Department diplomatic security agent who was part of the advance team reported hearing an unusual sound he believed was similar to what was experienced by U.S. diplomats in Cuba and China who later became ill. The agent immediately underwent medical screening — part of a new U.S. government protocol established to respond to such potential health incidents anywhere in the world. And while the president was flying to the Southeast Asian city state, the U.S. delegation preparing for his arrival was exchanging urgent messages with the State Department headquarters back in Washington, including the agency's Diplomatic Security and the U.S. Secret Service. It turned out to be a false alarm, according to four U.S. officials familiar with the matter, who were not authorized to speak to the matter publicly and spoke on condition of anonymity. But the rapid response underscored how