A Dutch Quandary Offers a Glimpse of a Deepening Problem for Europe

Just months ago, Geert Wilders was an anathema to most Dutch political parties.

A disruptive and divisive force on the far right for two decades, Mr. Wilders has said he wants to end immigration from Muslim countries, tax head scarves and ban the Quran. He has called Moroccan immigrants “scum.” His Party for Freedom has supported leaving the European Union.

But then Mr. Wilders won national elections convincingly in November. Nearly a quarter of Dutch voters chose his party, which won 37 of 150 seats in the House of Representatives, a huge margin by the standards of a fractious party system that rests on consensus and coalition building.

Since then, Mr. Wilders has become an unavoidable political force. “He is the biggest,” said Janka Stoker, a professor of leadership and organizational change at the University of Groningen, of Mr. Wilders. “They simply can’t ignore him.”

That quandary has made the Netherlands a test case for Europe as it grapples with the question of what to do with far-right forces that have advanced so far into the mainstream that they can hardly be considered on the fringe anymore.

Italy already has a hard-right leader, and the Swedish government depends on a party with neo-Nazi roots. The far right now represents significant parts of the opposition in France and Germany, forcing the question of how much longer it can be shunned.