His pioneering work in psychobiography was published during the last four years of his life and was way ahead of his time. In 1929 Clark published Napoleon: Self-Destroyed, the first book-size psychoanalytic study of Napoleon Bonaparte. In the last year of his life he published Lincoln: A Psycho-biography, another early work in this field. Clark fought some of the heated battles of the American psychiatrists against the American neurologists that were common in the first part of the twentieth century. Clark's reputation suffered when he was found to have plagiarized most of "Napoleon Self-Destroyed." Clark also was criticized for misunderstanding what Freud meant by what Clark referred to as "narcism."
Review of "Napoleon: Self-Destroyed", 1930, in the "Journal of Nervous and Mental Disease," 71 (3): 347-356. This critique seems to have been forgotten. See also letters in Jelliffe Papers, Library of Congress.