(29. März 2017) The arrest and subsequent execution of Mr. Tolkachev was the most damaging of a series of mysterious spy losses suffered by the C.I.A. in 1985. In fact, there was so much espionage activity between the C.I.A. and the K.G.B. that burst into public view in 1985 that it became known as the Year of the Spy.

But why?

Debate swirled inside the cloistered world of American counterintelligence. Could all the spy losses be blamed on C.I.A. incompetence? Or had they resulted from something more sinister, like a Russian mole inside the agency?

That 1985 debate has in some ways been mirrored in the public debate about the hacking of the D.N.C. during the 2016 presidential campaign.