IF ANY UNIVERSAL lesson may be drawn from modern European history, it is that evil cannot be permanently suppressed. Unreason recedes but invariably snaps back to challenge free societies. Today Europe may be at the precipice of such a resurgence, whose symptoms include a vicious anti-Semitism that frequently expresses itself as hostility to the State of Israel and an ascendant far right bent on restaging the previous century’s disastrous blood-and-soil nationalisms. The continent is also the site of a homegrown radical Islam inherently incompatible with the European Union’s lofty liberal ideals.