With almost 60% of the vote, Jeremy Corbyn was elected chairman of the Labour Party in September 2015. Since then, the reported expressions of antisemitism among a number of the party’s elected representatives have greatly changed the public attitudes of many British Jews and their leaders.Corbyn is an extreme leftist sympathizer of the genocidal antisemitic terrorist organizations Hamas and Hezbollah. Many in Labour consider him largely responsible for the party’s resounding defeat in the December 12th parliamentary elections. Corbyn has announced that he will resign as party leader in the near future. This is an appropriate occasion to assess the important changes in British Jewry’s attitudes over the past four years. Traditionally, the leaders of British Jewry maintained a rather low public profile. This made sense as Jews make up only about 0.4% of the country’s population. On issues of communal interests, leaders approached the authorities directly to obtain their support.According to former Labour officials who dealt with complaints in the party, antisemitism was rarely if ever a topic before Corbyn’s chairmanship. Yet, later research found that there had been some extreme antisemitic remarks under Corbyn’s predecessor, Ed Miliband. These mainly came from Muslim officials.The first complaints about Labour antisemitism after Corbyn’s election concerned a small group in early 2016 – the Oxford’s University Labour Club. Only key conclusions of the investigation of this body by non-Jewish Labour peer Baroness Royall were published. The full, initially covered-up report was leaked a few months later, probably by Baroness Royall.Additional information on antisemitism in Labour gradually emerged. Thereupon Corbyn charged the non-Jewish human rights expert Shami Chakrabarti with investigating it. Her report published on June 30, 2016, was poorly composed. She also showed major ignorance about antisemitism’s essence. Shortly thereafter, upon Corbyn’s recommendation, she became Baroness Chakrabarti. It remains unclear when that peerage was promised to her.The reaction of the Board of Deputies of British Jews – the official representative of the community – to the botched report was moderate. However, already in May 2016, Chief Rabbi Ephraim Mirvis said that the crisis engulfing Labour had “lifted the lid on bigotry.” After Corbyn’s conference on the Chakrabarti report on July 1, Mirvis said the chairman had caused “greater concern rather than rebuilding trust with the Jewish community.” Former chief rabbi Lord Jonathan Sacks called Corbyn’s words there “dehumanization of the highest order, an outrage and unacceptable.”Many of the early strongest attacks on Labour antisemitism came from individuals. David Collier wrote that it was clear that Corbyn’s issue with antisemitism “runs far deeper than a few counselors and MPs.” Another person who spoke out against Corbyn was David Hirsch. In September 2016, the small organization, Campaign Against Antisemitism, filed a formal complaint against Corbyn. It accused him and his allies of having a long association with antisemites.Some Jewish Labour MPs also started to expose the party’s antisemitism gradually. MP Ruth Smeeth walked out of Corbyn’s press conference on the Chakrabarti report after she was insulted by a reporter. Smeeth claimed that Corbyn had failed to intervene when antisemitic slurs were directed toward her in front of him.THE JEWISH Labour Movement was established in 1901. It has been affiliated with the Labour Party for about 100 years. Initially, when the party’s antisemitism came in the open, it tried to muddle through. In later years, it became a very tenacious anti-Corbyn force.Over the years many traditional Jewish Labour voters deserted the party. In April 2019, a survey by the Jewish advocacy group Jewish Leadership Council found that 87% of British Jews believed Corbyn to be antisemitic. Rather suddenly, in recent years many British Jews began speaking about possibly emigrating if Corbyn would be elected prime minister. The survey reported the number at 47%. Even if one doubts how many Jews would actually leave the UK in case of a Labour victory, the talking about it was a radical development.A meeting with Corbyn by leaders of the Board of Deputies and the Jewish Leadership Council in April 2018 concluded that Corbyn’s proposals “fell short of the minimum levels of action.” A few weeks earlier the two Jewish organizations wrote in an open letter, “Again and again Jeremy Corbyn has sided with antisemites rather than Jews.” On March 26, the Board of Deputies organized a demonstration outside Parliament in London.In July 2018, The Jewish Chronicle, The Jewish News and the Jewish Telegraph, all rivals, took the unprecedented step of publishing the same front page. It stated that this step was motivated by the “existential threat to Jewish life in this country that would be posed by a Jeremy Corbyn-led government.”The heaviest price for Jewish opposition against Corbyn has been paid by several Jewish MPs. Ruth Smeeth was not reelected in the recent parliamentary elections. Already at Labour’s annual party conference in September 2016 she had to arrive with a bodyguard after she had received 25,000 abusive messages. MP Luciana Berger received thousands of hate e-mails by April 2016, some of which threatened her with rape or murder. Later she left Labour and was afterwards defeated standing as a liberal Democratic parliamentary candidate. A third Jewish MP, Louisa Ellman, left the party in October 2019. The only remaining Jewish female Labour MP is Dame Margaret Hodge. In 2018, she called Corbyn a racist and antisemite in the parliament’s lobby.Soon Corbyn will resign. Chief Rabbi Mirvis has stated that antisemitism is there to stay. In the process, British Jewry’s public attitudes have greatly changed. What came out of the bottle cannot be pushed back in.The writer is the emeritus chairman of the Jerusalem Center for Public Affairs. He received the Journal for the Study of Antisemitism’s Lifetime Achievement Award, the Simon Wiesenthal Center’s International Leadership Award and the Canadian Institute’s for Jewish Research’s International Lion of Judah Award.