For decades, the American Right and Left argued about the degree to which the KGB infiltrated the U.S. political and scientific establishment. The Right said "A lot"; the Left said "Much less than you think." Both sides did a lot of finger-pointing and, sadly, slandering. Things got very ugly. At the crux of the problem, though, was a lack of reliable information about exactly what the KGB had done and how successful (or not) they had been in recruiting Americans.
That changed in the mid-1990s. The United States de-classified the results of the "Venona Project,"–an intelligence initiative that involved the surveillance of secret Soviet cable traffic during World War Two–and Alexander Vassiliev, a Russian journalist, made his notebooks on KGB activities in the U.S. available to researchers. For the first time, scholars such as John Earl Haynes and Harvey Klehr could measure the success of KGB spying in the U.S. during the Cold War.
The results are eye-opening, as Haynes and Klehr explain in Spies: The Rise and Fall of the KGB in America (Yale University Press, 2009). Though it's probably unwise to speak of "winners and losers" in the debate over KGB spying in the U.S., Haynes and Klehr show that the Soviets, though often bungling, had done a pretty fair job of tapping sympathetic American Leftists and stealing American secrets. That said, they also discovered that some of those the Right had accused of spying (e.g., Robert Oppenheimer) were in fact innocent.
This is a fascinating book and should be read by everyone interested in Cold War espionage.