The astonishing landslide victory of extremist Jeremy Corbyn in the leadership election for Britain’s Labour Party is being widely interpreted as likely to ensure that their Conservative foes will remain in power for a long time. The Tories are happy about this and mainstream Labour activists sadly agree that their party — which seemed invincible a decade ago at the apex of Tony Blair’s prime ministership — has rendered itself unelectable. That’s good news for those who hope to keep the “special relationship” between the U.S and Britain alive (a group that does not appear to include President Obama) and believe a responsible Conservative government in London will help preserve the alliance. But no one should be celebrating Corbyn’s triumph, least of all Britain’s Jewish community. Even if Corbyn never gets closer to the prime minister’s seat on the government’s front bench in Westminster than his current perch as leader of the opposition of parliament, the elevation of a person who holds the views that he has embraced sends a chilling message for the future of British Jewry and that of Europe as a whole at a time of increasing anti-Semitism.

There are many commentators that see Corbyn’s victory as being of a piece with the rise of anti-establishment candidates in the United States on both the right and the left. It is true that anger at the perceived failure of government and the loss of faith in the political class is fueling the popularity of both Donald Trump and Bernie Sanders. But while there is much to worry about in both of those candidacies, such simplistic analogies are as likely to mislead as to inform. For all of the negative consequences of Trump’s popularization of nativism, Corbyn’s embrace of crackpot extremist stands that are integral to the rising tide of European anti-Semitism must be viewed in an even more serious light.

Corbyn’s CV of outrageous positions are well known. He has stated that he considers the United States to be the moral equivalent of ISIS. He is a fervent opponent of Israel and openly sympathetic to Hamas and Hezbollah. He has supported those who promote 9/11 truther myths and praised vicious anti-Semites. He called Osama bin Laden’s death “a tragedy” and campaigned for the release of terrorists convicted of attacking Jewish targets. And he has praised Russian and Iranian propaganda channels and even hosted a show on Iran’s Press TV. In other words, he is a typical example of the way left-wing Western European elites have crafted a bizarre alliance with radical Islamists that has created such a hostile atmosphere for Jews and friends of the Jewish state. Muslim immigrants to Europe have brought with them their own traditions of Jew-hatred and prejudice. But they have found partners among Western intellectuals, academics and others who falsely believe Zionism is a vestige of European imperialism — the cardinal and original sin in the view of the continent’s elites — rather than the national liberation movement of the Jewish people. The result is a toxic mix that has brought anti-Semitism back from the margins of European society in the aftermath of the Holocaust to being something that can be expressed unashamedly in the public square.

So while it is comforting to think that Labour will suffer negative electoral consequences in the future, that is actually beside the point. One would hope that Corbyn would moderate his views in his new post and perhaps he will to some extent though his talk about having a special envoy to the Jewish community may do more harm than good. The problem is that his elevation legitimizes views that ought to be treated as belonging solely in the fever swamps of the far left and far right in a way that they hasn’t been the case since before the Holocaust. Even if Corbyn minds his manners — and that seems unlikely given his history — his victory shifts the pendulum of public opinion in a way that cannot be entirely compensated for by future Tory victories. It allows all sorts of haters in Britain and elsewhere to feel that much more comfortable about opposing the war on Islamist terrorists or to target Israelis and Jews.

Even more to the point, it cannot help but undermine efforts to mobilize Europe to support the struggle against ISIS that the U.S. is already only pursuing in a half-hearted manner. Nor is it likely to stiffen the resolve of Britain or other nations to hold Iran accountable after the implementation of the nuclear deal that the West has signed with Tehran.

One may hope that Corbyn’s win is just an aberration that won’t serve as the harbinger of worse to come. But with anti-Semitism, operating behind the thin veil of anti-Zionism, already being expressed more brazenly in Britain and throughout Europe, there is good reason to worry that the virus will continue to spread, rather than be contained.