PARIS — The five million Muslims of France and the 500,000 Jews of France eye each other with unease. Muslims complain that questioning the Holocaust is forbidden by law but insulting the Prophet Muhammad is not. Two weights, two measures, they say. Sephardic Jews in suburbs of hostile Muslims feel they are back in the North Africa their forebears fled.

Muslims, often encountering daily prejudice, are susceptible to old libels about Jewish wealth, influence and power. Four Jews — Yoav Hattab, Yohan Cohen, Philippe Braham and François-Michel Saada — are shot dead in a kosher supermarket by a jihadi fanatic and Paris, to some Jews, looks like the epicenter of a war between Islam and the West. Mosques are defaced. Synagogues are protected by soldiers. Muslims are ghettoized in drab projects, asked to pray in disused barracks.

Jewish descendants of Holocaust survivors hear cries of “Death to the Jews” in the streets of Paris, chanted by so-called anti-Zionists. Muslims speak of the need for 2,000 more mosques, a demand that is fodder for the far-right National Front. Some Jews vote with their feet. They leave.

This is not the whole story, or even most of the story, of France today, but it is enough of the story to make anyone wonder: What would happen if there were another terrible incident, say the kidnapping and beheading of a prominent Jew?