To be clear, Von Papen had been pushing the Enabling Act from Hitler's very first cabinet meeting, so it wasn't the case that he suddenly lost influence or left the scene after March 1933. But with Hitler's efforts at Gleischaltung, or Coordination of the Reich, Papen's star set rapidly over the course of 1933-34: the ace up his sleeve had been control of the government of Prussia, which he himself as Chancellor deposed in July '32. Hitler merely undercut the lander goveremts by installing parallel Nazi governments.

Then in June, '34, Papen goes to the ailing Hindenburg with hat in hand to admit that his scheme of controlling Hitler has utterly failed, and Hindenburg charges him with fixing it. With the help of his secretary, the conservative intellectual Edgar Jung, he writes a speech critical of the Nazi regime which he delivers at the University of Marburg. Aimed mainly at the rowdiness of the SA, whose leader Ernst Rohm had been calling for a second revolution, it struck a chord with Germans exhausted by SA street violence. Hitler retaliated by killing off Rohm and Jung - the Night of the Long Knives, after which Hindenburg, the military and the masses came around again fully to Hitler.

Papen's bolt was shot, but Hitler either believed he would be useful, or else that he was too popular to kill, or both. He first sent him to lead negotiations with Austria. There, Papen pursued a policy of union (which had been the implicit German policy since Bruning) but things fell apart quickly after the assassination of PM Dolfuss. Finally, Hitler hijacked the negotiations and forced Anschluss by martial means.

Finally, Hitler packed Papen off as Ambassador to Turkey - a not insignificant power courted by Germany, the USSR and the west throughout the war. But as German fortunes changed, the chances of Papen's mission succeeding grew ever slimmer. He stayed there until 1945.