I think gwern is teasing us: there is no such quotation in Sluga's Heidegger's Crisis, or at least I cannot find it in the Google Books version. Perhaps gwern has taken the Wittgenstein/Malcolm story and swapped Britain for Germany to make a point about the universal applicability of the philosopher's rebuke. But for what it's worth: * The date in the Heidegger version of the story is very suspicious: in 1939 Churchill was First Lord of the Admiralty; he did not become Prime Minister until May 1940 and it is only with hindsight that we see his significance (even in 1940 most political actors seem to have thought that Lord Halifax would be a better choice for Prime Minister than Churchill). * The version of the anecdote featuring Wittgenstein and Malcolm is backed up by a citation to Malcolm's Ludwig Wittgenstein: A Memoir where Malcolm quotes the letter from Wittgenstein at length. Also, the 1939 date for the original quarrel about "national character" is a better fit to this story, because in 1939 no-one could doubt the significance of Hitler, and assassination attempts on Hitler were by that point a fairly regular occurrence.