This paper deals with the position of medievalists when confronted with modern anti-Semitism. It is about their contribution to reflection on the forms of anti-Jewish hostility and the permanence of these forms. In fact, in the long period of time from the Middle Ages to today, echoes crop up which medievalists finds themselves compelled to assess: are they recurrences, revivals, adaptations, alterations, or mutations? By taking into account recent reflections on historical regimes of temporality and causality, this paper aims to show that the issue of the interplay between context and legacy regarding anti-Jewish hostility recurs because of current events and is dominated, accordingly, by the obsession with teleology. The evolution of David Nirenberg’s historiographical positions, between Communities of Violence (1996) and Anti-Judaism (2013), shows how the perception of present-day events may impact choices of sources, temporality, and methods. The case of the forced baptism of Jewish children finally enables us to observe that in the same way as the racial component existed before modern anti-Semitism (as testified by the medieval motifs of the fluxus sanguinis or the limpieza de sangre), religious anti-Judaism persisted well beyond the Christian world and right into the middle of the twentieth century. The study carried out in a long-term perspective reveals that the argument of Judaism being a danger for children, which underlies the issue of the forced baptism of Jewish children, is a Christian construction that does not require Christianity to be maintained. The implicit, but obvious connections between the new forms of anti-Jewish hostility and those in the past finally show that the link established between past and present is not an outright historiographical artefact.