But with the Alternative for Germany sucking voters from Ms. Merkel’s party, conservatives are pushing the party to attribute a more central role to Germany’s cultural identity. Leitkultur has reappeared in Christian Democratic speeches and working papers. Ms. Merkel used the term approvingly while campaigning in March.

There’s a difference between Leitkultur and the Alternative for Germany’s einheimische Kultur — in the Christian Democratic version, the nativist element is weak; Islam is not a target, at least explicitly. Still, the reintroduction of the concept at a time when the Alternative for Germany is promoting its cultural version of the Aryan nation is as strategically clever as it is dangerous: The Christian Democrats are whitewashing the far-right version of the Cultural German.

While the political cost is high, the concept of Leitkultur is useless. Attempts at legally defining and protecting “German culture” often verge on the absurd. In April, after reports that some public cafeterias no longer served pork out of respect for the dietary restrictions of their Muslim customers, the Christian Democrats in the state of Schleswig-Holstein introduced a proposal to preserve pork dishes in public canteens. “We must not allow for a minority to determine what the majority eats,” a local Christian Democrat said. Some of the reports proved false. The “schnitzel law” caused snickering — and was rejected.

Asked in 2000 what he thought went into German Leitkultur, Mr. Merz pointed to the Constitution and to women’s rights. But it’s no use making refugees swear an oath on women’s rights. Germans won’t control what they think. But Germany can help them understand the laws protecting women’s rights — and reinforce them.

A modern nation state cannot be built on an ontological notion of who belongs and who does not, whether it’s outright ethnic or pseudo-cultural. It needs to build on the notion of the nation as a community — a community including those who were born here, those who came to stay and those who will stay for a while and then return to their homes. The rights and duties of the members of this community should be defined by their achievements, and by the rule of law — not by whether they eat schnitzel or wear a head scarf.