Eugene Rabinowitch intended the Bulletin of the Atomic Scientists to be an institution of scientific internationalism in the early cold war. He hoped that the Bulletin might serve, faute de mieux, as a site of international contact that would allow his vision of the scientific life to contribute to peace and stability in the shadow of the atomic bomb. Domestic anticommunists, however, envisioned the relation of science to national security and the role of the scientist quite differently. Protecting a sense of oneself as a scientist was consequently a feat of endurance, as Rabinowitch’s experience with the Bulletin shows.