Glenn Simpson, the former Wall Street Journal reporter turned high-priced “oppo” merchant, didn’t like to think of himself as a private investigator. He preferred to describe what he and his firm, Fusion-GPS, did as “journalism for rent,” an activity a class above spying, because a journalist can’t just say what he or she thinks. “You have to prove it,” Simpson said. “And that imposes a discipline to the investigative process that people in other fields don’t really absorb… When you’re a spy,...
