David Bohm (1917-1992) was an American theoretical physicist who would later become a citizen of the United Kingdom.
After finishing his undergraduate degree at the Pennsylvania State University in 1939, Bohm arrived at the University of California, Berkeley on a seemingly meteoric rise. However, during this same period he became affiliated with the Communist Party, which would ultimately undermine his chances for success in the United States.
Like many others, Bohm was recruited by J. Robert Oppenheimer as a graduate physics student at the University of California, Berkeley to become a part of the Manhattan Project. Bohm would never make it to Los Alamos though, as General Leslie Groves flatly denied him a security clearance. Bohm's history with radicalism--he was a regular attendee of Berkeley Communist Party meetings and at one point dated the future Betty Friedan--caused too much of a risk in Groves's mind. As such, it was impossible for him to directly contribute to the Manhattan Project. Yet his graduate thesis, written on the collisions of protons and deuterons, was deemed pertinent to the project, and was classified. Lacking the proper clearance, Bohm was barred from accessing his own research. No less than Oppenheimer himself had to testify to the university that Bohm had adequately completed his degree.
The charges of radicalism would continue to follow Bohm after the war. After refusing to testify about his Communist ties before the House Un-American Activities Committee (HUAC), he was eventually arrested in 1950. Though he would be acquitted for contempt of Congress soon after, he decided his career would benefit from foreign citizenship. In 1951, he left the United States to do research in Brazil, before eventually settling in the United Kingdom. There he would have a distinguished career as a physicist.