On December 23, 1953, in what it claims were the "interests of national security" the Atomic Energy Commission (AEC) temporarily suspended Oppenheimer's security clearance. At the height of U.S. anticommunist feeling, Oppenheimer was accused of having long-term associations with the Communist Party. His opinion toward the development of the hydrogen bomb was also cited: that Oppenheimer had continued to oppose the development of the hydrogen bomb even after President Truman had ordered a program to go ahead. And they claimed that his opposition had retarded the progress of the project.
Suspicions about his patriotism had dogged Oppenheimer for about a decade. In part they dated back to an incident during the war, when a professor of French, Haakon Chevalier, had tentatively approached Oppenheimer about passing information to the Soviets. Oppenheimer hadn't reported the incident immediately, and when he did, the story he told changed several times.
Most of the scientific community was distressed by the news of Oppenheimer's impending security hearings. The hearings opened on April 12, 1954, and lasted for four weeks. The security board majority found that Oppenheimer was a loyal citizen and that the nation owed him "a great debt of gratitude for ... magnificent service." But it claimed that his "continuing conduct and associations reflected a serious disregard for the requirements of the security system." The board did not recommend reinstating his security clearance.
The hearing was a sad episode in American history. It was personally devastating to Oppenheimer and divided the American scientific community. Oppenheimer retired from public life and spent the rest of his life continuing to be the director of the Institute for Advanced Study at Princeton. Eventually, the injustice was recognized. In 1963, he was awarded the nation's highest distinction in nuclear science, the Enrico Fermi Award. Oppenheimer died from cancer in 1967.