This is the final episode in a three-part series about "Oppenheimer" and the historical debates raised by the blockbuster film.

By the time he left office in early 1961, President Dwight Eisenhower had overseen the expansion of the nation's nuclear arsenal to 20,000 weapons. The United States had dramatically outpaced the USSR in the opening years of the arms race. The Soviet Union had roughly 2,000 bombs after the first full decade of the Cold War. The "missile gap" notwithstanding, both superpowers had more than enough nuclear firepower to destroy the world many times over, and this was the actual point of the policy of "mutually-assured destruction." Robert Oppenheimer and like-minded scientists had hoped to avoid this outcome by trying to influence national defense policy after the Second World War. Christopher Nolan's blockbuster film "Oppenheimer" shines a light on the physicist's opposition to the H-bomb program and his support for international arms control and openness, rather than secrecy, in national security policy. In this episode, historian Gregg Herken, author of "Brotherhood of the Bomb," discusses whether the U.S. missed a chance to avoid an arms race and decades of Cold War by ignoring Oppenheimer's advice in the late-1940s and early 1950s.