Vicious antisemitism has long been present on the radical Right. It has been growing also on the radical Left. And it’s a cornerstone of radical Muslim movements. Although these three sources of antisemitism in our world today come from very different traditions, they are increasingly sharing ideas and tactics, reinforcing a wave of hate, bigotry and racism.In recent years, North America has joined Europe to witness a growing alliance between radical Muslims and radical leftists. Radical Muslims stone women, execute gays, trample on minority and human rights and abhor feminism. On paper, the far Left should be appalled by this ideology, but these unlikely allies happily cast aside their differences because they share common hatred for Western influence in the world, pluralistic nationalism, freedom of speech, tolerance, and vile antisemitism.How does the radical Left turn a blind eye to radical Islam’s very bigoted ideas, such as its treatment of women and minorities? How can it ignore radical Muslims’ conviction as to the superiority of Islamic morals and culture? It infantilizes Muslims and portrays Islam as a monolithic block. In doing so, it fails to distinguish between mainstream Muslims and radicals, and tokenizes them as a “people oppressed by the West.”In the radical Left’s warped and ahistorical worldview, Israel is a colonialist oppressor targeting Muslims and – straight from the Elders of Zion itself – Jews are an all-powerful group who are at fault for every problem in the Middle East and in the world.This alliance is typified by political activist Linda Sarsour, one of the organizers of the Women’s March on Washington, who is now hailed on the Left as a feminist leader, despite her admiration for the vile misogyny of Sharia law. She called a Jewish journalist a member of the antisemitic alt-right. She opened her “jihad against Trump” speech by thanking Siraj Wajjah, an unindicted co-conspirator in the 1993 World Trade Center bombing. She has praised Saudi Arabia’s treatment of women. Yet, she is held up as a role model for women on the Left.And this alliance is growing. Last month, leftist students at Tufts University published a “Disorientation Guide,” which attacked the university’s Hillel and called Israel a “white supremacist” state. It exposed the depth of antisemitism among leftists on college campuses, and demonstrated how these groups use the same rhetoric as radical Muslim groups that call Israel a colonial occupier. One of the guide’s writers claimed this was not antisemitic because she was Jewish.A similar guide at New York University myopically condemns Israel, referencing the country 55 times – more than the number of references to “Trump,” “alt-right,” “racism,” “fascism,” “white supremacy” and “socialism” combined. Two recent rally events in Chicago further illustrate this trend: one, the Chicago Dyke March earlier this year – an event created to celebrate the LGBT community – expelled three people for having Stars of David on their pride flags, combining two symbols central to their identity. A few months later, at the Chicago SlutWalk – an event intended to oppose sexual assault – Zionists who marched were derided for trying to participate and condemned by organizers. The organizers then encouraged the walkers to attend a speech by Rasmea Odeh – a Palestinian terrorist convicted of killing two Jewish students, still believes her actions were justified and who was recently deported from the US.This strange allegiance between Islamic radicals and radical leftists was famously on display during the Iranian revolution of the late Seventies – where the Grand Ayatollah Khomeini overthrew the moderate shah with the support of leftists and Islamists, and in turn was quick to empower the radical Muslims and decimate the radical Left.The 3,000-old Jewish population of Iran, some 100,000 Jews, could sense the inherent antisemitism of the radical leftists and their hatred of the West, before and during the Iranian revolution and emigrated in large numbers as fast as they could – mostly to the US and Israel.Just as the far Left has a history of vilifying the nation-state of the Jewish People (and the Jews who support it), the Right has colluded with radical Muslims to spread its pure hatred of Jews and the desire to brutally subjugate – or murder – the Jewish People.Radical Islamic nationalists also have a history of collaborating with the Right when they can – the Grand Mufti of Jerusalem told Adolf Hitler that Germans and Arabs have the same enemies – “the English, the Jews, and the Communists” – and the prime minister of Iraq initiated the Farhud, a horrific pogrom, under Nazi influence and allegiance. Today, the rhetoric of neo-Nazis is rife with conspiracy theories and centuries- old stereotypes about blood libel, and echoes the rhetoric of radical Islamist terrorists – and even radical Muslims.What’s most concerning about the rise of antisemitism is how the ideology has entered the mainstream.For instance, Vermont Senator Bernie Sanders recently campaigned for UK Labour Leader Jeremy Corbyn, who has worked closely with antisemitic conspiracy theorist Paul Eisen, author of a blog titled “My Life as a Holocaust Denier.” Sanders wouldn’t campaign for a socialist who was a sexist, a racist, a homophobe, or Islamophobe, but he was willing to campaign for an antisemite, because leftist organizations encourage antisemitism.Radical Muslims are focused on destroying and delegitimizing Israel – the historic homeland of the Jewish People — and they fan the flames of antisemitism wherever they can to reach that goal – whether among those working to stop racism in present-day America or working to grab power in 1940s Iraq, or boycotting Israel through the BDS movement. By allying with the radical Left, they are building a coalition that seeks to destroy Western values of freedom, democracy and tolerance – the foundational principles of America and of Israel, the only democracy in the Middle East. The growth of this alliance and the mainstreaming of antisemitic leftism – especially on college campuses – threatens not only our way of life in America, but the future of the Jewish People around the world.The author is an Israeli-American philanthropist, national chairman of the Israeli-American Council, real estate entrepreneur and president of the Adam and Gila Milstein Family Foundation.