
A member of Denmark’s Parliament and, he hopes, mayor of this commuter-belt town west of Copenhagen, Mr. Dencker is furious that some day care centers have removed meatballs, a staple of traditional Danish cuisine, from their cafeterias in deference to Islamic dietary rules. No matter that only a handful of kindergartens have actually done so. The missing meatballs, he said, are an example of how “Denmark is losing its identity” under pressure from outsiders.

It is also Europe’s new reality. All over, established political forces are losing ground to politicians whom they scorn as fear-mongering populists. In France, according to a recent opinion poll, the far-right National Front has become the country’s most popular party. In other countries — Austria, Britain, Bulgaria, the Czech Republic, Finland and the Netherlands — disruptive upstart groups are on a roll.