Teller immigrated to the United States in the 1930s, and was an early member of the Manhattan Project charged with developing the first atomic bombs. During this time he made a serious push to develop the first fusion-based weapons as well, but these were deferred until after World War II. After his controversial testimony in the security clearance hearing of his former Los Alamos colleague J. Robert Oppenheimer, Teller was ostracized by much of the scientific community. He continued to find support from the U.S. government and military research establishment, particularly for his advocacy for nuclear energy development, a strong nuclear arsenal, and a vigorous nuclear testing program. He was a co-founder of Lawrence Livermore National Laboratory (LLNL), and was both its director and associate director for many years.