The article argues that we are witnessing a lethal “mainstreaming” trend across Europe that involves previously taboo ideas, frames, and practices becoming the new “common sense” for growing sections of European politics and societies. As in the case of the dramatic slide into dictatorship and the spread of virulent anti-Semitism in the 1930s, the divisive ideas of the contemporary far right vis-à-vis minorities, immigrants, and Muslims/Islam in particular have been crossing multiple boundaries—between “extremist” and “mainstream” politics and voters, between taboo and legitimate views, as well as between countries. As in the 1930s, the success of this putative “far-right contagion” today owes at least as much to the weakening defenses or cynical opportunism of the mainstream as to the dynamics and appeal of the radical right's ideas themselves.