What has caused the deeply alarming upsurge in anti-Semitism across the West? As many have observed, there are three principal sources: the political left, Islamic culture and neo-fascist or white-supremacist cults.

One further factor, though, is crucial. Never disappearing altogether, anti-Semitism can be kept to a low level by condign social disapproval that deems anti-Semites to be totally beyond the pale.

If, however, that social stigma is lifted and society tolerates, excuses or sanitizes anti-Semitism, then it roars out of control.

That’s precisely what is now happening. In America, astoundingly, it is being facilitated and mainstreamed by Democratic Party grandees.

Look at what happened over remarks made by Michigan’s Democratic Rep. Rashida Tlaib. The congresswoman, whose Arab parents were born in Ramallah, said thinking of the Holocaust gave her a “calming feeling.”

This, she said, was because her Palestinian ancestors “lost their land and some lost their lives, their livelihood, their human dignity, their existence in many ways” in order to “create a safe haven for Jews, post-the Holocaust, post-the tragedy and the horrific persecution of Jews across the world at that time. And I love the fact that it was my ancestors that provided that, right, in many ways. But they did it in a way that took their human dignity away and it was forced on them.”

This was a vicious travesty of history. Wickedly, she presented Palestinian Arabs as victims of the Holocaust’s victims. The reality was that those Arabs were actually hopeful ancillaries to the Nazi genocide of the Jews.

Far from giving their lives to provide safe haven for the Jews, as she claimed, the Arabs of Palestine did everything they could to stop them from coming in and slaughtered as many as possible—all to prevent the Jews from obtaining the homeland that could have saved thousands from the Nazi genocide.

Much worse still, they intended to perpetrate a Final Solution for the Jews in Palestine and beyond. The Grand Mufti of Jerusalem, Haj Amin al Husseini, formed a pact with Hitler that if he won the war, the Mufti would ensure that every Jew in the Middle East was exterminated.

As the Nazis stepped up their persecution of the Jews in Europe, Arab storm-troopers marched in Palestine shouting “Heil Hitler” and branding the Jews “the human sexual disease” and “a menace to all mankind.”

The Palestinian Arabs have never stopped waging that war of extermination. They write the Jews out of their own history in the land to which the Arabs lay false and ahistoric claim.

They vandalize priceless archeological sites to destroy the physical evidence that Israel was the Jews’ national kingdom centuries before the Arabs invaded. They teach their children to kill Israelis, steal their land and hate Jews.

Indeed, they have never stopped bombing, shooting, knifing and decapitating Jews in Israel. Mahmoud Abbas, who worships al Husseini, recently admitted the Palestinian Authority’s central role in promoting attacks on Israelis when he justified paying the families of terrorists.

His spokesman, Nabil Abu Rudeina, said: “It is impossible to send a soldier to war and then not take care of his family. We are talking about someone who acts on our behalf and receives orders from us.”

The ancestors of today’s Palestinian Arabs were Hitler’s army in the Middle East; and their descendants can justly be regarded as the last undefeated front in the Nazi war against the Jews.

For making such remarks, Tlaib should be thrown out of Congress. As U.S. President Donald Trump rightly said about “her horrible and highly insensitive statement” on the Holocaust: “She obviously has tremendous hatred of Israel and the Jewish people.”

But instead of treating her as a pariah to be shunned, the Democrats have circled the wagons around her. The Speaker of the House, Nancy Pelosi, said that “desperate attempts to smear” Tlaib and misrepresent her comments were “outrageous.”

Tlaib was neither smeared nor misrepresented. It was Pelosi’s defense of her remarks that was outrageous. Worse, this is now part of a pattern by Pelosi of sanitizing and normalizing Islamic antisemitism.

Although Minnesota Democratic Rep. Ilhan Omar accused Israel of “hypnotizing the world” and prayed that “Allah awaken the people and help them see [Israel’s] evil doings,” Pelosi appointed her to the House Foreign Affairs Committee. And after Omar claimed that Jews use their money to suborn American politicians in the interests of Israel, Pelosi played down the remark.

She also invited a radical Islamist imam, Omar Suleiman, to deliver the noon prayer in Congress.

Suleiman has not just compared Israel to Nazis and incited violence against Israelis. As detailed by Islam researcher Andrew Bostom, he has a long history of virulent anti-Semitic comments, in line with Islamic religious texts, depicting the Jews as cosmically evil, incurring God’s wrath so they were transformed into apes and pigs and so forth.

Yet this is the man that the Democrats not only honored in Congress, but whose behavior they defend by smearing as “Islamophobes” those who dare call out his bigotry.

In Britain, the struggle against Labour anti-Semitism is getting nowhere at all, despite repeated outrage and even resignations by a number of decent Labour MPs.

A major part of the problem is that this derangement is by no means confined to the supporters of Labour’s far-left leader Jeremy Corbyn. This was shown by last weekend’s revolting anti-Israel hate-fest in London. Chanting demonstrators brandished posters declaring that Jews control the media, Jews are the new Nazis, Jews have no right to a state, Jews bring anti-Semitism upon themselves and so on.

Yet faced with this chilling display, the media could barely bring itself to shrug. This is largely because progressive people refuse to acknowledge that their signature Palestinian cause—so revealingly exposed by the mind-bending distortions of Rashida Tlaib—is the new anti-Semitism.

And that’s because they refuse to acknowledge that Palestinianism itself is fundamentally anti-Jew.

This denial of a most inconvenient truth—that the Arabs’ hatred of Israel derives from their murderous hatred of the Jews—was illustrated by one aspect of a BBC documentary last week about the border riots in Gaza.

In it, a Gazan boy says “the revolutionary songs excite you, they encourage you … to rip a Jew’s head off.” But, instead of accurately translating the Arabic word Yahud that he and others used for Jew, the BBC mistranslated it as “Israeli.”

The BBC insists that this was “both accurate and true to the speakers’ intentions.” This is simply untrue. In Arabic, yahud means “Jew.” When Arabic media refer to Israel, they use that word in Arabic letters.

A chant frequently heard among Islamic religious extremists is Khaibar, Khaibar, ya Yahud, Jaish Mohammed, sa yahud, which means “Jews, remember Khaibar, the army of Mohammed is returning.”

Anyone who reads Islamic religious texts can see that hatred of the Jews is embedded in Islamic religion and culture. Yet in America and Britain, this is all but unsayable.

Anyone who points out that Islamic society is fueled by hysterical and obsessional anti-Semitism is deemed to be Islamophobic—not least by prominent British Jews.

Astoundingly, they equate Islamophobia—the term designed to silence criticism of the Islamic world—with anti-Semitism. So they remain silent about this major threat to themselves from the Muslim community, the group of which the left will permit no criticism, while inflating the threat from “the right,” the group the left blames for all the ills of the world—and in which it preposterously lumps together white supremacists, anyone who criticizes mass immigration and all those who voted for Brexit.

Denial of Palestinian and Muslim antisemitism is legitimizing, mainstreaming  and fueling anti-Semitism in the West.

When confronted with their own bigotry, people like Tlaib and Suleiman claim that the real problem of anti-Semitism comes from “the right.”

And which groups in both America and Britain hand them this particular “Get out of jail free” card so they can continue to escalate the climate of Jew-hatred? Why, the left, of course—and the Jews.

Melanie Phillips, a British journalist, broadcaster and author, writes a column for JNS every two weeks. Currently a columnist for “The Times of London,” her personal and political memoir, “Guardian Angel,” has been published by Bombardier, which has also published her first novel, “The Legacy,” released in April 2018. Her work can be found at her website, www.melaniephillips.com.