In the United States, in fact, border crossings have been low for years, and in Europe they are now far lower than they were at the peak of the refugee crisis a few years ago. Rather, the migrant crisis is a backlash against migrants and refugees, and the political fights and extreme policies that has set off.

The anger, research suggests, often stems less from migration specifically than from a broader anxiety over social change. When people feel a sense of threat or a loss of control, they sometimes become more attached to ethnic and national identities.

For some people, the antipathy is explicitly racial. But for many others, the mere fact of cultural change itself can be unsettling. Immigration, unauthorized or otherwise, is just one of the changes that bring about a feeling of the loss of control. Economic dislocation, changes in social hierarchies and demographic change can all produce the same effect.

But when asylum seekers arrive without permission or warning, that can add to the sense of anxiety by making the border — perhaps the most obvious symbol of national identity and territorial protection — seem weak.

On both sides of the Atlantic, migrants and asylum seekers have become, for many voters, a symbol of the political establishment’s failure to protect them and their interests.