In his vast, impressive book Inside the Centre: The Life of J. Robert Oppenheimer, Ray Monk tells of how, amazingly, despite being the head of the Manhattan Project to develop the atomic bomb, Oppenheimer was persistently investigated under suspicion of being a communist, mainly because in his younger years he had some contacts with communists, and because post-WWII he consistently aired the view, considered un-American, that the science behind the weapons should be open, and that America should be sharing information with the Soviet Union. His reasoning was that the science made possible weapons of such destruction that only open cooperation would ensure they were never used. And Oppenheimer consistently called for restraint, once the seriousness of the Cold War arms race became apparent after WWII. (No wonder – subsequent tests of hydrogen bombs yielded explosions 1000 times bigger than the Hiroshima bomb, making them almost impossible to use in a purely military sense.)
Monk repeats the facts that Oppenheimer, despite his particular political bent, was consistently a patriotic American (which Monk partly ascribes to Oppenheimer’s interest in the Hindu Bhagavad Gita, which emphasises duty) and that there was never much to incriminate him. Yet he was investigated by the HUAC (whose members included, famously, Richard Nixon), and was consistently tailed by the FBI (FBI Director Hoover was certainly suspicious of him, but his suspicion seems to have remained luke-warm, due to the fact that no compelling new evidence turned up, despite all the digging). Such was the paranoia of Cold War USA.