Then something happens. A conflict comes into focus that, beyond its particulars, raises the question of the ultimate compatibility of Islamic communities in Western environments. An issue that, most comfortably, is kept vague, suddenly demands that Europe — in this case, the Netherlands — draw the line. But where is the line?

What has taken place here is that Frits Bolkestein, the former leader of the Liberal Party, which now heads the Dutch government, has advised “recognizable Jews, orthodox Jews” that their children should emigrate from the Netherlands to Israel or the United States. He said, “I see no future for them here because of anti-Semitism, above all among the Moroccan Dutch, whose numbers continue to grow.”

The remark last month twice shocked the Netherlands.

There was the statement itself, resounding in the context of a national history in which almost the entire pre-World War II Jewish community of 150,000 was wiped out by the Nazis.

More, there was Mr. Bolkestein’s view that the Dutch state was unlikely to deal successfully with the problem and his uncertainty that the Dutch people would demand its resolution. These were matters, he told me later, that reflect his profound and overarching concern about the long-term influence of Muslim populations on all of European society.

This dark vision has particular impact here because of Mr. Bolkestein’s reputation among many of the Dutch as kind of seer concerning Muslim immigration. When he suggested in a speech in 1991 that integration had to mean compromises from newcomers concerning their old identities, he was denounced as a bigot. In the intervening 20 years, large parts of the Dutch political spectrum, and much of Europe’s, have evolved toward a position (closer to his) that regards respect of national law and tradition as more necessary than any further European accommodation to a growing Muslim community.