I just find it interesting that there are all these points in history when everything swings on one decision. There are so many “if only’s” to the story of Trump that it would make wonderful reading if I didn’t have to live through it.
If we’re going to have a thread about spies in QT3, we have to least mention Robert Hanssen. After all, he was the subject of the movie – all together now – Breach! (that and he was one of the most damaging spies in US history).
I think it depends on how you rate harmful. Aldrich Ames probably got more people killed or jailed than any other spy. The Walker group gave the USSR the Navy’s most important secrets. So who’s the most harmful I’d say is debatable.
And, of course, Klaus Fuchs gave the USSR pretty much all the details of Fat Man. However, it’s difficult to say, in the long run, how harmful that was. The Soviets had a better bomb on the drawing boards, but Beria, whose paranoia was on par with Stalin’s, insisted they copy Fat Man.