 The episode aired after a summer in which the fallout shelter had loomed large in national discourse, due to the Berlin Crisis of 1961.Meeting with U.S. President John F. Kennedy in Vienna, Soviet Premier Nikita Khrushchev insisted—not for the first time—that NATO troops withdraw from Berlin, handing over the city to an independent, Soviet-aligned East Germany.Khrushchev explicitly threatened thermonuclear war if the United States refused to relent.