Introduction: An Amendment at the Crossroads of Nuclear Power and Presidential Fallibility begins in medias res with US Senator Birch Bayh’s observations of President John F. Kennedy’s decision-making, which averted a nuclear showdown between the United States and the Soviet Union in October 1962. Traditional histories of the Twenty-Fifth Amendment (which lays out a plan for presidential continuity: presidential succession, vice presidential vacancy, and presidential inability) argue that President John F. Kennedy’s assassination was the reason for the development of the amendment in 1963, but they do not consider the pervasive nuclear anxiety inherent in American politics and culture during the Cold War that acquired additional urgency in the shadow of the Cuban missile crisis. “We needed a plan,” said Bayh, the architect of the amendment, “We had to make sure there was always somebody who had his finger on the [nuclear] button”(Birch Bayh, Interview with Author, November 11, 2014.). The Introduction delineates the structure of the book which, using previously unmined sources, tells the story of the amendment’s drafting, ratification, and after-effects through the lens of nuclear anxiety, a presidential assassination transition, and a democracy in crisis.