Jeff Stein, an investigative reporter specializing in U.S. intelligence, defense, and foreign policy, is author of the blog Spy Talk. He was an Army intelligence case officer in Vietnam.

As long as there have been spies, there have been spy scandals. Usually, however, it's because a senior official got hooked up with an enemy spy, most famously like British Secretary of War John Profumo, who in 1963 was "dating" an alleged call girl who was also involved with a Soviet naval official suspected of being a spy. Down he went.

That was a long time ago. And in the half century since, there's no known record of a Western intelligence chief resigning over the love of a person not his wife.

Until Friday, that is, when the once unsinkable David Petraeus announced he was resigning because of his "extremely poor judgment by engaging in an extramarital affair."

The target of his affection was quickly identified as Paula Broadwell, the author of a recent hagiographic book about him, All In: The Education of General David Petraeus.

According to veteran intelligence reporter Ron Kessler, who has a well-drilled pipeline into the FBI, the resignation of Petraeus "followed an FBI investigation of many months" prompted by the interception of an email he sent to the "girlfriend."

Nothing remotely like that has touched the 19 CIA directors who preceded Petraeus...