Too horrible to believe

In the summer of 1943 Supreme Court Justice Felix Frankfurter, probably the most eminent American Jew and a devoted Zionist, went to the Polish embassy in Washington to meet the Polish socialist Jan Karski, another death-camp escapee. When Karski finished describing what he had seen at Belzec, Frankfurter paced in somber silence for ten minutes. "I am unable to believe you," he said to Karski at last. "Felix, you cannot tell this man to his face that he is lying," the Polish ambassador interjected. "I did not say that this young man is lying," Frankfurter replied. "I said that I am unable to believe him. There is a difference." Frankfurter extended both arms and waved his hands. "No, no," he said, and walked out.

David M. Kennedy, Freedom from Fear: The American People in Depression and War, 1929-1945 (New York: Oxford Univ. Press, 1999), ch. (Kindle locations 14136-41) (citing Kai Bird, The Chairman: John J. McCloy and the Making of the American Establishment (New York: Simon & Schuster, 1992), 206)