This memo is described by Longerich here:
Hitler`s motives become apparent from a memo written by the representative for the Eastern Ministry in Hitler`s headquarters, Koeppen, on 20 September. Koeppen wrote that the Envoy von Steengracht (representative of the Foreign Office in the headquarters of the Führer) had told him that Hitler was considering the question of postponing possible "Pressalien" (i.e Repressalien; reprisals) against the German Jews "for a [sic] eventuality of an American entry into the war".This memo reveals that the killing of German Jews was tied to US entry into the war. This may at first glance appear to support the idea that no decision to kill the Jews was therefore taken before December. However, this idea would pre-suppose that Hitler had no expectation of the US entering the war until they actually did so, when in reality the very fact that Hitler had the 'reprisal' thoughts in his mind shows that his expectation was very real by September at the latest.
This memo can cast further light on Hitler's thinking when used in conjunction with Goebbels' diary entries for August 19-20, 1941, which quote Hitler's thoughts at a point that was a month prior to the Koeppen memo. Browning summarizes the entries here:
"The Führer is convinced that his Reichstag prophecy is coming true; that should the Jews once again succeed in provoking a world war, this would end in their annihilation. It is coming true in these weeks and months with a certainty that appears almost sinister. In the east the Jews are paying the price, in Germany they have already paid in part and they will have to pay still more in the future.” Concerning that fateful future, Goebbels learned when (“Moreover the Führer has promised me that I can deport the Jews from Berlin immediately after the end of the eastern campaign.”), where (“in the east”), and more vaguely the ultimate fate of the deportees (“Then they will be worked over in the harsh climate there.”).These entries show that Hitler had been harbouring the view for quite some time that Jews would die in large numbers, either during a long war or after a short war (the latter being preferable). However, as of August, their deaths were expected to be attritional, presumably through a combination of shooting, forced labour and starvation in a climate such as that of Siberia. Furthermore, their deaths are clearly linked with those of the Soviet Jews:
In the east the Jews are paying the price, in Germany they have already paid in part and they will have to pay still more in the future.Hitler's thoughts in August therefore only differed from the final fate of the Jews in the facts of the locations and methods of murder. A genocide in which approximately half of the victims died in gas chambers in death camps was the result of the inability of the Germans to pursue the originally planned attritional method due to the war not developing as successfully as they desired, but it is false to assume that the gas chambers were a genocidal "quantum leap" from the previous attritional plans.
In conclusion, therefore, the effects of the Soviet counter-offensive and US entry on the one hand, or Hitler's "victory euphoria" on the other, upon the Final Solution, did not determine the initial murderous impulses that resulted in the gas chambers. They shaped the direction that the murderous impulses took, in forcing the Nazis to look for solutions primarily within Poland than in Siberia, but they did not turn a resettlement into a mass murder of millions of Jews. The resettlement was always going to be a mass murder of millions of Jews.
In other words, the escalation in killing that took place after the decisions of 1941 was not a 'moral escalation' (or, rather, a further moral descent) by Hitler. He had already arrived, mentally and morally, at the point where the extermination of Jewry, by whatever means available, was not only thinkable but desirable.