Final answer:
Oleander's sense of betrayal at Nuremberg was rooted in the "stab-in-the-back" myth which alleged Germany was sabotaged from within during WWI. This myth was part of the Nazi ideology and contributed to the justification of their war crimes, for which leaders like Oleander were held accountable at Nuremberg.
Step-by-step explanation:
Heck's "overwhelming sense of betrayal" at Nuremberg likely refers to Otto Oleander's feelings of betrayal due to the "stab-in-the-back" myth perpetuated by German military leaders. These leaders, including Hindenburg and Ludendorff, as well as the Kaiser, propagated the false narrative that Germany could have continued fighting in World War I but was sabotaged from within by Jewish and communist conspirators. Oleander and other Nazis, including Hitler, felt betrayed by this notion, which fueled their rise to power and their subsequent actions during World War II.
The sense of betrayal was compounded at the Nuremberg Trials, where the enormity of the Holocaust and the actions of the Einsatzgruppen, including those under Ohlendorf's command, were brought to light. Ohlendorf himself was eventually found guilty of war crimes and executed. His expression of a sense of betrayal likely reflects a sense of abandonment by the very superiors and ideology that drove his actions.