By the time a Chinese spy balloon crossed into American airspace late last month, U.S. military and intelligence agencies had been tracking it for nearly a week, watching as it lifted off from its home base near China’s south coast, an earlier sighting of the balloon than has been previously known. U.S. monitors watched as the balloon settled into a flight path that would appear to have taken it over the U.S. territory of Guam. But somewhere along that easterly route, the craft took an unexpected northern turn, according to several U.S. officials, who said that analysts are now examining...