On November 18, French President François Hollande spoke in Israel’s Knesset and showered praise on Israel and on the Jewish people in general. He also made special mention of the French expatriate community in Israel, and assured his audiences — in France as well as in Israel — that he would “not rest in fighting anti-Semitism.”

His host, Prime Minister Benjamin Netanyahu, was equally gushing, as the recently renewed romance between Jerusalem and Paris went on public display. Old tiffs over Israeli-Palestinian relations were brushed aside, while Hollande and Netanyahu’s opposition to the Iranian nuclear program was highlighted.

But Netanyahu certainly knows, as must Hollande, that there was an elephant in the Knesset chamber. The silent presence was not Iranian President Hassan Rowhani or Palestinian Authority President Mahmoud Abbas — or even President Obama. Rather, it was the nearly half-million-strong French Jewish community and the sense of deep concern (“dread” might not be too strong a term) that pervades it.

Netanyahu knows — having been informed in Jerusalem and having seen and heard it firsthand in Paris — that French Jewry has lost faith in France and is looking to move. Indeed, many young French Jews have already relocated to London and New York, where newly formed French Jewish expat communities are growing rapidly. But if and when a large-scale outflow occurs, its destination will certainly be Israel.

In one respect, the Jewish youngsters are part of a wider phenomenon, because the economic prospects for young people in France are now so bleak that, perhaps for the first time in modern French history, the idea of mass emigration has gone mainstream.

But the Jews, as usual, have additional issues. Unlike the general population, which has begun to think about emigration as an option only in the past year or two — and even then, only for educated youngsters — voices in the French Jewish community have been arguing for the past decade that there is no Jewish future in France.

The assault has come from a few directions. France’s large Muslim community has turned increasingly anti-Semitic as it becomes more alienated from French society. This has combined with a more traditional form of anti-Semitism that rears its head during periods of prolonged socioeconomic crises and now has found political form in Marine Le Pen’s extreme right party. Then there are the proliferating legislative efforts across Europe to make Jewish animal-slaughtering procedures or circumcision illegal as violations of animal or children’s rights.

French Jews may be receiving the brunt of these threats at the moment, but they are pan-European in scope. In every European country, at least one of the three threats is on display, to a degree powerful enough to make that country’s Jews increasingly uncomfortable. How many will leave, how soon and under what circumstances —voluntarily or otherwise — will depend on the intensity of the socioeconomic crisis and its political fallout. But in view of the fact that most countries, including traditional havens such as the United States, Canada and Australia, are increasingly picky regarding whom they allow in, most of the Jewish emigrants will come to Israel.

The mildly good news is that in recent months, the Israeli government, the Jewish Agency for Israel and the other key entities involved in immigration and absorption have belatedly awoken to the increasingly dire realities in Europe. The prospect of a large-scale aliyah from Western European — hence supposedly prosperous and liberal — countries is boggling the bureaucrats’ minds, because it renders obsolete the basic policy and planning assumptions underlying their activities.

Fortunately for Israel and for the prospective immigrants, the country is now rich enough to handle even a major influx. But the inevitable disruption this will cause and the need to divert significant resources to the task of absorption — as well as the claims that “the immigrants are taking our jobs” despite overwhelming evidence that immigration is a net positive for the recipient economy — ensure that there will be a fierce debate within Israeli society and politics over whether to maintain an open door for all Jews. This will be a reprise of earlier rounds of the same debate, in 1949 and in 1990.

At the end of this debate the door will stay open, because that is Israel’s ultimate raison d’etre. But when the question moves from whether to how, and it becomes apparent just how costly it will be to take in potentially hundreds of thousands of European Jews — many of them old, sick or poor — then Israel will seek partners in this task.

There is, however, only one relevant potential partner, American Jewry. But how will the largest Diaspora community respond to a major crisis in the second-largest Diaspora community? With very few exceptions, American Jews, their leaders and representative organizations have no knowledge of, or interest in, European Jews. Their view of the world has two focuses, the primary and dominant one being the United States and the secondary one being Israel. In between, from New York to Tel Aviv, stretches a large black hole encompassing countries and communities to which they have given no serious thought since the 1950s.

American Jewry is soon going to be faced with a challenge that will require it to stand up and be counted — as Jews. There will be no universalist peg on which to hang this impending campaign, only the basic Jewish imperative that Jews in more fortunate circumstances must come to the assistance — financial, political and even physical — of Jews in trouble.

Whether American Jews can rise to this challenge is something that, unfortunately, we are likely to find out quite soon. The gathering storm in Europe is, already, the greatest opportunity in a generation or more for American Jewry to shake off its ennui and, as a collective, do great things for the Jewish people.

Pinchas Landau is an independent economic consultant based in Jerusalem.