Why FDR did not assassinate Hitler

As many history buffs already know, U.S. Pres. Franklin Delano Roosevelt expressed joy on behalf of the American people in a letter to Canadian Prime Minister Mackenzie King for the way war was averted by the signing of the Munich Agreement on Sept. 29-30, 1938. FDR wrote to King on Oct. 11 that he was privileged to play a role in the "amelioration of the European crisis." Ten days earlier, immediately after the signing of the Munich Agreement, FDR had written to a cousin-in-law that he had had "a pretty strenuous two weeks," including a "stupid and continuing runny nose." He then added that he had "wanted to kill Hitler and amputate the nose" but that today, Oct. 1, 1938, "I have really friendly feelings for the latter [the nose] and no longer wish to assassinate the Fuehrer." FDR was jesting in private, but how many Czechs knew that the U.S. president gave up on the idea of assassinating Hitler because he was so thrilled by the signing of the Munich Agreement?