This paper will examine a notable parallelism between the writings of Katherine Anne Porter and Hannah Arendt. They both show a similar interest in tracing out how the good can collude in political evil, particularly as this was demonstrated in the interwar period of the European dictatorships. In several interviews and letters, Porter claimed that this “collusion” was the central moral crux of her work, and it was one that informs her last major work, Ship of Fools (1962), as well as earlier shorter fiction such as “Theft,” “Flowering Judas” and “Noon Wine.” Hannah Arendt, in her post-war writings such as The Origins of Totalitarianism and Eichmann in Jerusalem, also posed similar questions to those of Porter about the acquiescence of the ordinary or liberal citizen in the criminality of the state. Arendt's concepts of “radical evil” and of “the banality of evil” can be brought into productive comparison with Porter's dramatization of “collusion,” particularly in her Weimar narrative of Ship of Fools. Both writers sought to intervene in the post-war American intellectual debate about the Holocaust, and both insisted on the primacy of the ethical response in the age of totalitarianisms. They also had a common philosophical source for their writings in Augustine's concept of the will (although there is perhaps no evidence that they directly interacted with one another's thought). This paper intends to bring Porter into the contextual framework provided by Richard H. King's Arendt in America (2015), especially since King does not bring up the case of Porter in his very detailed study.