During the Cuban Missile Crisis, he persuaded the President of Senegal, Léopold Sédar Senghor, to deny the Soviet Union landing rights to refuel its planes. From 1964 to 1969, he was the American Minister to the Court of St. James, or DCM of the American Embassy in London, when David K.E. Bruce was the American Ambassador there. Many of the leading British political figures of the period, including Ted Heath and Roy Jenkins, had been Kaiser's friends when he studied Politics, Philosophy and Economics at Balliol College, Oxford, from 1936 to 1939. While he was Minister, he entertained Groucho Marx, Robert F. Kennedy, and Richard Nixon, among many other famous cultural and political figures. He lived at Wychwood House, his official American residence on Cottesmore Gardens in Kensington.