There was widespread paranoia in the United States throughout the 1950s about the possibility of Soviet espionage, and these new revelations certainly seem to indicate that not all of it was unjustified. There is little doubt, of course, that the Red Scare—with the prodding of Sen. Joseph McCarthy—cast its net too wide in its frantic attempts to find communist sympathizers. No atomic bomb secrets leaked from blacklisted movie stars, after all. There is also no evidence that Robert Oppenheimer, the director of the Manhattan Project, ever provided assistance to the Soviets, though he was controversially stripped of his security clearance while overseeing the development of the hydrogen bomb.
If Stillman and Reed are right, though, there were some who did aid the Soviets. And it may have taken only one man in the right place to help them build their bomb.
Corrected on 01/07/09: An earlier version of this article misstated the year the Soviet Union tested its first thermonuclear bomb. The first Soviet test was in 1953, one year after the first U.S. test in 1952.