Published as having been made in an (August 1936) interview http://www.greatwar.nl/frames/default-churchill.html with William Griffin, editor of the New York Enquirer http://en.wikipedia.org/wiki/National_Enquirer, who was indicted for sedition http://www.time.com/time/magazine/printout/0,8816,773366,00.html by F.D.R.'s http://www.whitehouse.gov/history/presidents/fr32.html Attorney General Francis Biddle http://www.usdoj.gov/osg/aboutosg/biddlebio.htm in 1942. In a sworn statement before Congress in 1939 Griffin affirmed Churchill had said this; Congressional Record (1939-10-21), vol. 84, p. 686. In 1942, Churchill admitted having had the 1936 interview but disavowed having made the statement (The New York Times, 1942-10-22, p. 13).
In his article "The Hidden Tyranny," Benjamin Freedman attributed this quotation to an article in the isolationist http://www.time.com/time/magazine/article/0,9171,795133,00.html publication Scribner's Commentator in 1936. However, that magazine did not exist until 1939. He may have gotten the date wrong or might have been referring to one of its predecessors, Scribner's Monthly http://cdl.library.cornell.edu/moa/browse.journals/scmo.html or Payson Publishing's The Commentator http://www.time.com/time/magazine/article/0,9171,765655,00.html.
Disputed
