One group, however, poisoned the planet with another idea. To Hitler, says Snyder, “It was the Jew who told humans that they were above other animals, and had the capacity to decide their future for themselves.” To Hitler, “Ethics as such was the error; the only morality was fidelity to race.” Hitler, who did not become a German citizen until 11 months before becoming Germany’s chancellor, was not a nationalist but a racialist who said “the highest goal of human beings” is not “the preservation of any given state or government, but the preservation of their kind.” And “all world-historical events are nothing more than the expression of the self-preservation drive of the races.”

Now, assume, reasonably, that Iran’s pursuit of a potentially genocidal weapon will not be seriously impeded by parchment barriers such as the recent nuclear agreement. And assume, prudently, that the Iranian regime means what it says about Jews and their “Zionist entity.”

Then apply Snyder’s warning: Ideas have consequences. The idea of anti-Semitism is uniquely durable and remarkably multiform. It can express a mentality that is disconnected, as in Hitler’s case, from calculations of national interest.