In an extraordinary departure from tradition, Britain’s Board of Deputies, the country’s highest Jewish communal authority, which prides itself on maintaining a strictly apolitical stance on a wide number of issues, issued a sternly worded letter to Jeremy Corbyn and the Labour Party this weekend. Its subject line says it all: “Enough is enough.”Corbyn, the letter states, “did not invent” the form of politics that systemically fails to take anti-Semitism seriously, “but he has had a lifetime within it, and now personifies its problems and dangers. He issues empty statements about opposing antisemitism, but does nothing to understand or address it. We conclude that he cannot seriously contemplate antisemitism, because he is so ideologically fixed within a far left worldview that is instinctively hostile to mainstream Jewish communities.”Again breaking with tradition, the Board of Deputies called for a mass demonstration of British Jews and their friends inside and outside the Labour Party in front of Parliament, scheduled for this afternoon.We stand with them, and we commend the Board of Deputies for their clarity and courage. Still, observing the situation unfold, we should also remember that what we’re watching is a tragedy. As recently as the premierships of Tony Blair and Gordon Brown, British Jews could feel that radical anti-Semites and violent champions of Hamas and Hezbollah were confined to the Labour party’s radical fringe. It seemed clear that British Jews, despite being the victims of long-standing and embedded discrimination, and targets of violence from some sectors of society, might feel welcome both in the Labour Party, the community’s traditional home, as well as by the Tories.No such luck: Again and again, Corbyn and his allies in the party’s leadership and base have effectively sided against the Jews, allowing and endorsing the most vile slurs, and making it clear that their own progressive ethos considered straight-up anti-Semitism as an acceptable, or even palatable, sentiment, that progressive Jews must swallow in order to remain in the party — and even then, they should be expected to submit to regular abuse. The Labour Party is now lost to so many Jews, and with it the feeling that they are afforded the same rights and protections as other Britons.Could the same happen here? Our first answer is no. The Democratic Party is nowhere near as diseased as Labour. Too many prominent Democrats are Jewish. No, it can’t happen here.But that might be simply a matter of time. What remains so astonishing about Labour’s disintegration is how quickly the party became a place where anti-Semitism is promulgated not in secret but in the open. What was once a hidden vice is no longer a cause for shame but rather of dithering, equivocation, and pointless rationalizations. Anti-Semitism simply, and frighteningly, has become if not an admirable stance, then certainly one that is tolerable.We saw the same thing happen with Louis Farrakhan this month, when—rather than exploding in shame and clear, unambiguous denunciations—too many of his supporters on the left limply justified their affiliation with a rank bigot. Beneath the endless high-profile blather about needing to understand the complexity of the bigot and the “good work” that some of his followers do in urban communities, the message was crystal clear: Farrakhan, and the entire package of what he represents, including open and vicious anti-Semitism, is more important to some people than “the Jews” are.This week, Tablet will be running a series of pieces about Farrakhan. Refusing to condemn people like him for his hateful views is how the slide towards unreason begins; it ends, as it did this week in London, with the Jews rising in anguish and despair against a major political party. Unless we’re vigilant, it can happen here.