Soviet intelligence operations during WWII and after were phenomenally successful whether it was our home grown traitors like Hiss, White, etc.; or in Britain with the Cambridge 5 and the deep penetration of MI5 & MI6; and my particular favorite Sorge in Japan, a man who's spying altered the course of the war.
I strongly believe the Soviet vipers in our and British governments were never completely uprooted. Just a thought.