Even before J. Robert Oppenheimer's first days at Los Alamos, the U.S. government had suspicions about his loyalties. And the doubts followed him until he was finally denied his Q clearance in 1954.

Like many liberal intellectuals of the time, Oppenheimer was quite taken with the idealism he believed to underpin the new Soviet state. He also feared for the safety of family members still living in Hitler's Germany. In the 1930s, bolstered as well by a loathing of Nazism, many Americans still living through the disillusionment with capitalism brought on by the Depression joined communist organizations and donated to causes supported by the Communist Party of the U.S.

In 1936, while teaching at Berkeley, Oppenheimer fell in love with a woman named Jean Tatlock, a sometime Communist Party member. She introduced Oppie, as he was known, to a series of friends who were later branded as fellow travelers. In the same year, his brother Frank, also a physicist, met and married a young radical, and they quickly joined the Communist Party.

Four years later, Oppenheimer married Katherine Harrison--his first marriage, her fourth; one of her former husbands had been a Communist Party member who had persuaded her to join. Throughout his years on the Manhattan Project, security officials kept probing Oppenheimer and his colleagues for security leaks. Oppenheimer was frequently evasive and on occasion dishonest in his accounts of meetings with suspected communists, but no leaks were detected until after the project was completed. The Soviets, after all, were America's allies during the war, and concern about their acquiring U.S. atomic secrets was secondary to the mission of beating the Axis.

After that goal had been achieved, Oppenheimer urged sharing atomic secrets with other countries, including the U.S.S.R., and eventually came to oppose the development of the H-bomb. His former Los Alamos colleague, Edward Teller, was infuriated by Oppie's doubts about the "super," as the thermonuclear device was called, and Teller's testimony before the Personnel Security Board of the Atomic Energy Commission was vital to the essentially political decision to revoke his clearance.

Curiously, at the same time that it denied him clearance, the board essentially exonerated Oppenheimer from any suspicion of espionage. The majority report declared him a "loyal citizen" and praised his "unusual ability to keep to himself vital secrets."