It was considered one of the CIA’s worst failures in decades: Over a two-year period starting in late 2010, Chinese authorities systematically dismantled the agency’s network of agents across the country, executing dozens of suspected U.S. spies. But since then, a question has loomed over the entire debacle. How were the Chinese able to roll up the network? Now, nearly eight years later, it appears that the agency botched the communication system it used to interact with its sources, according to five current and former intelligence officials. The CIA had imported the system from its Middle East operations, where the...