Oppenheimer met and began to date 22-year-old Jean Tatlock, a shy and beautiful young woman who had bouts of depression similar to those that once plagued him. A recent graduate of Vassar College and a devotee of Jungian psychoanalysis, Tatlock had joined the Communist Party, albeit more from aversion to social injustice than from devotion to Marxist precepts. The romantic relationship grew serious and intense as both wrestled with inner demons. Tatlock drew Oppenheimer into her circle of ardent left-wing activists. In addition, Oppenheimer met Haakon Chevalier, a professor of French literature at Berkeley, a doctrinaire Marxist, and a devoted Communist.

Oppenheimer’s budding romance with Tatlock and friendship with Chevalier developed against the backdrop of the Spanish Civil War in Europe. Like many leftist intellectuals, Chevalier found his political heartbeat quickening with the outbreak of that war in 1936. Although Oppenheimer never joined the Communist Party—or at least no evidence exists to prove that he did—his left-wing political sympathies nonetheless deepened as the dramatic events of the late 1930s unfolded; he made financial contributions to various left-wing causes and took an active role in a local teachers’ union. His colleague Ernest Lawrence found Oppenheimer’s politics both counterproductive and annoying.