Signal group chat is only the latest dangrous intelligence lapse

In 2012, three men on a late-night walk in Toronto discussed plans to conduct a major terrorist attack. Two of the men were al Qaeda-linked radicals. The third was an undercover FBI agent, secretly recording the conversation. 

Their scheme: Drill a hole on the path of the Maple Leaf train traveling between Toronto and New York City, derail the passenger cars and kill as many civilians as possible. 

An unprecedented level of cooperation between 15 U.S. and Canadian agencies halted the men in their tracks...