Yosef Mendelevitch, who is coming to next month's Limmud conference, is one of the heroes of the refusenik movement who defied the oppressive yoke of Communism. His Jewish activism did not stop after his release from Soviet jail. He became an Orthodox rabbi in Israel, sporting a long, white beard. In an interview last year, about the translation into English of his book Unbroken Spirit, he said, "American Jewry saved me; now I hope so to save American Jewry."
The largest diaspora Jewry has always thought of itself as a generous uncle helping less fortunate relatives, not a community in need of salvation. But a recent article by two American Jewish academics has raised serious questions about its future. Writing in the online magazine Mosaic, Professors Steven Cohen and Jack Wertheimer declared, "American Jews now stand on the precipice of a demographic cliff and the choice before them is simple: either fall off, or turn around."
Accusing American Jewish leaders of a lack of urgency in the face of crisis, they rest their case on an analysis of last year's Pew survey of American Jews. Not only intermarriage, but non-marriage and low birthrates are depleting the majority non-Orthodox community. More than two million people of Jewish parentage no longer identify as Jews. The number of non-Orthodox Jews under 17 is only two-thirds of those in the 40-57 age bracket.
Religiously identifying Jews are far more engaged with Jewish life than secular/ cultural Jews, not simply in ritual practice but also in donating to Jewish causes or connection with Israel. Intermarried families are "considerably less likely" to join synagogues, contribute to Jewish charities or identify with Israel. But only one in five children of intermarried families is being brought up religiously Jewish, while one in three is not being raised as any kind of Jew at all.
As a remedy against further disintegration, Cohen and Wertheimer suggest a concerted educational drive - such as greater enrolment in day schools or youth summer camps and better campus programming - and encouraging conversion among the intermarried. Not everyone, it has to be said, agrees with their warnings of doom but the historian of American Jewry Jonathan Sarna commented that their broad argument "should indeed set off alarm bells across every part of the organised Jewish world".
More than two million people of Jewish parentage no longer identify as Jews
Their image of the cliff recalls the dramatic advert with which Chief Rabbi Sacks launched his Jewish Continuity organisation in order to reverse the decline of British Jewry in 1993; it depicted lines of young people queuing like lemmings to tumble off the edge of a precipice, with the headline "Today, we'll lose another 10 Jews."
So how has British Jewry fared since? The survey published by the Institute for Jewish Policy Research (JPR) this year shows a mixed picture. On the one hand, the younger generation are more religious than their parents or grandparents - but the figures almost certainly reflect the extraordinary growth of the strictly Orthodox who form a larger slice of British, than American, Jewry.
Intermarriage, which rose steadily through their latter half of the 20th century, appears to have flattened out to a rate of around 25 per cent over the past decade. The JPR research matches the American findings; intermarried families are less practising and communally involved than all-Jewish families.
But nearly half of British Jews who were raised traditional (members of an Orthodox synagogue but not strictly Shabbat observant) or Progressive have switched allegiance; some have moved right in religious terms, but most left. That shrinking middle-ground has led to a greater number of Jews who view themselves as cultural or secular, compared to 20 years ago. From Cohen and Wertheimer's perspective, that must seem a worrying trend, since the more religiously attached you are, they argue, the better your chances of Jewish continuity.
On the potential credit side, far more children propotionately go to Jewish day schools in the UK than they do in the USA. Here, of course, faith schools are state-subsidised, whereas in America they are private and beyond the reach of many parental pockets. It may take another generation before we can tell if the great Jewish school boom over the past two decades has paid off. British Jewry can also boast the highest diaspora participation in Israel summer tours, sending around half of its 16-year-olds there each year.
While many pin hopes on day schools, a more recent JPR study offers a cautionary note. Measuring the impact of Jewish education on the identity of Jewish students, JPR found that although education made a positive difference, it was only "modest" –- and far less influential than family upbringing, for example whether they had Friday night dinners or ate kosher.
The most powerful Jewish experiences, according to this study, turned out to be gap years in Israel or time in yeshivah or seminary. Such intensive programmes are costly, however, and perhaps not so attractive for young people faced with university tuition fees and anxieties about jobs and housing. Finding cheaper alternatives will be a challenge.
But this latest research reminds us that Jewish education doesn't stop at school. Investing in the post-18s is important if we want the next generation to resist the seductive kiss of assimilation.