An AfD supporter at a rally during regional elections in Magdeburg, Germany. Photo by Craig Stennett / Getty Images Donald Trump arraigned, Boris Johnson expunged, Silvio Berlusconi dead. You could say this was a bad fortnight for the populists. The backlash against them is in full swing. But so is the backlash against the backlash. In Europe, at least, populism is on the rise again. It will get worse. The best way to think about populism, and political trends in general, is to distinguish between causes and triggers. The rise in immigration that accelerated in the last decade was a...