One explanation for this is that many of the drivers of change within Muslim communities that have paved the way for greater hostility toward Jews have had an equally corrosive effect on public opinion at large. The rise of identity politics has helped create a more fragmented, tribal society, and made sectarian hatred more acceptable generally.

At the same time, the emergence of “anti-politics,” the growing contempt for mainstream politics and politicians noticeable throughout Europe, has laid the groundwork for a melding of radicalism and bigotry. Many perceive a world out of control and driven by malign forces; conspiracy theories, once confined to the fringes of politics, have become mainstream.

Anti-Semitism has become a catchall sentiment for many different groups of angry people. The distinction between anti-Zionism and anti-Semitism has eroded, as many see Israeli action in terms of grand conspiracies. Thus someone can imagine that Israel would build gas chambers on the West Bank if it could get away with it.

Perhaps in no country are the corrosive effects more visible than in France. And perhaps no figure better represents the character of the new anti-Semitism than the stand-up comic Dieudonné M’Bala M’Bala, notorious for popularizing the “quenelle,” a hand gesture that, for some, is an expression of hatred for the system, and for others, an anti-Semitic taunt. In reality, it is both: Dieudonné’s popularity shows how inchoate anger against “the system” and anti-Semitic sentiment can all too easily become fused, and his success rests on his ability to blur the two.

But Jews are not the only object of this free-floating rage. The Pew survey showed not just that anti-Semitism had increased throughout Europe, but also that the “publics that view Jews unfavorably also tend to see Muslims in a negative light.” The fusion of xenophobia, conspiracy theory, identity politics and anti-politics that has nurtured the new anti-Semitism has also cultivated hostility to Muslims. The Pew report found that in every country surveyed, “Opinions about Muslims in almost all of these countries are considerably more negative than are views of Jews.”

Against this background, what is troubling is that many who rightly challenge anti-Semitism do so in a way that fuels anti-Muslim prejudice. Many commentators talk of anti-Semitism as an almost wholly Muslim problem, and have used the growth of anti-Semitism to question the wisdom of allowing Muslim immigration to Europe. Others suggest that Muslim support for Palestine shows that Muslims cannot be truly integrated into Western societies.

Such arguments only entrench further hostility toward “the other,” and so inflame not just anti-Muslim but anti-Jewish sentiment, too. Israel’s action in Gaza should not be a moral shield for complaisance with anti-Semitism in Europe. But neither should anti-Semitism be a moral shield for the justification of anti-Muslim prejudices. Bigots on both sides need to be held to account.

Kenan Malik, a writer, lecturer and broadcaster, is the author, most recently, of “The Quest for a Moral Compass: A Global History of Ethics.”