Presupposition is used mainly in connection with implicit historical and political references to situations in Cuba or West Berlin, where Kennedy does not go into detail but touches the surface, assuming the audience will infer the rest. Knowledge of the policies of the Soviet Union and the fundamentals of the Cold War are also a prerequisite.
Metaphors such as arms race, used as pawns or fruits of victory would be ashes in our mouth are effective and naturally raise the sophistication of the speech, which always stays within the formal framework of such discourse. As for conceptual metaphors already used in Truman’s speech, Kennedy does not shy away from presenting the threat of attack on the US soil as a global issue. Unlike Truman though, Kennedy has the advantage of claiming that nuclear weapons pose a threat to the entire world. Of course, the validity of the “unmistakable evidence… of offensive missiles” in Cuba, which Kennedy claims to have gained can never be verified.