Is it possible to be anti-Semitic and pro-Israel at the same time? Your answer depends on how you define the terms. As Toni Morrison wrote, "definitions belong to the definers, not the defined." If you define anti-Semitism solely as criticism of Israel, the answer is dangerously simple, and it can excuse the racism of a white nationalist on the grounds that he supports Israel.

The controversial appointment of Stephen Bannon as Donald Trump's chief strategist shows how difficult it is to disentangle definitions of anti-Semitism from attitudes towards Israel, and makes it all the more urgent to do so.

Very few Jewish organisations - among them is The Anti-Defamation League (ADL) - have condemned the appointment of a man who "presided over the premier website of the 'alt-right' - a loose-knit group of white nationalists and unabashed anti-Semites and racists."

Along with smaller liberal Jewish groups, the ADL defines anti-Semitism as a form of prejudice, hatred and exclusion that intersects with other kinds of racism and bigotry.

In contrast, Bannon's defenders hold an exclusive monopoly on the meaning of anti-Semitism. The Zionist Organization of America lauds him as "the opposite of an anti-Semite", because "every article [on Breitbart News, the website Bannon ran] about Israel and the Palestinian Arabs he has published are all supportive of Israel." The evidence that Breitbart News is not anti-Semitic, is simply that it hurls that label at those who oppose the Israeli occupation and support Palestinian rights.

Shifting definitions

Hardline defence of Israel immunises Bannon from any accusation of anti-Semitism. Praising him as a "passionate Zionist", his advocates reprise a long-derided defence against racism: "Why, some of my best friends are …" They discount Bannon's negative statements about Jews as the exaggerated rant of an ex-wife, or perhaps the off-the-cuff equivalent of Trump's "locker room talk".

The ADL bears some historical responsibility for the powerful conflation of anti-Semitism with criticism of Israel.

In 1974, the ADL published The New Anti-Semitism, a book that radically redirected the concept away from prejudice against Jews and towards animus against the State of Israel, and simultaneously, away from the political right towards the left.

"Classic anti-Semitism" was on the wane, the book claimed. The old stereotypes espoused by groups such as the John Birch Society and the Ku Klux Klan seemed an anachronistic throwback in an America where Jews had made it.

The new dangers of anti-Semitism instead came from the radical left and black power movements, which refused to understand Jews alone as victims of persecution. In the context of the Vietnam War and the 1967 Six-Day War, some leftists condemned Israeli imperialism and championed Palestinian resistance. The ADL read this as sign of a virulent new strain of anti-Semitism on the rise.

From the 1970s to our own time, the ADL has wielded this definition to monitor groups supporting Palestinian rights, especially Arab-American and Muslim organisations. Ironically, the "new anti-Semitism" seems to be discovered again and again, decade after decade.

It has come to a hysterical crescendo in the 21st century. To name just a few titles, there's The Real Anti-Semitism in America (1982), The New Anti-Semitism (2003); The Return of Anti-Semitism (2004); Resurgent Anti-Semitism (2013).

The 'new anti-Semitism' is immutable, according to its definers. They no longer understand it as a prejudice that can be educated away, a stereotype that can be challenged, or discrimination that can be remedied by law.

The argument is always the same: Israel is the victim of international persecution as the "Jew among nations". The circle of persecutors has been expanded beyond 1960s radicals to include the United Nations and Third World nations, which condemned Zionism as racism in the 1970s, and to the mainstream media in the 1980s, for broadcasts of Israeli brutality in Lebanon and during the First Intifada. New accusations of new anti-Semitism started targeting human rights groups and the Nobel Peace Prize in the 1990s.

The term became capacious enough to include Jewish critics of Israel, who had once been considered merely "self-hating". Since 2001, definers of the new anti-Semitism have circulated anti-Muslim stereotypes of "Islamofascists" who purportedly fuse anti-Semitism with Anti-Americanism.

Excusing bigotry

This "new anti-Semitism" is immutable, according to its definers. They no longer understand it as a prejudice that can be educated away, a stereotype that can be challenged, or discrimination that can be remedied by law - the ADL approach to anti-Semitism in the 1940s and 1950s.

OPINION: How Europe's far-right feasts on Trump's victory

Consequently, they have no hope that criticisms of Israel might abate if its policies change, and they believe that murderous hatred of Jews is the only obstacle to peace in the Middle East.

To be sure, some critics of Israel do also express hostility towards Jews. But Bannon's legitimation of a white nationalism that hates Jews but admires Israel has forced a reckoning with the single-minded meaning of the "new anti-Semitism" as criticism of Israel.

It is time to dismantle this exclusive definition and undo the damage it has done to "the defined".

Even now, the right is pushing back on criticism of Bannon by tarring as anti-Semitic progressive leaders and movements so essential to the current struggle against Trump.

We cannot allow the charge of anti-Semitism to muzzle critics of Israel, nor blind allegiance to Israel to excuse bigotry. Americans must stop the new administration from justifying racism, xenophobia and Islamophobia on the grounds that it supports Israel.

Amy Kaplan is professor of English at the University of Pennsylvania, and author of The Anarchy of Empire in the Making of US Culture. She is currently working on a book on the history of the changing ways that Americans have viewed Israel.

The views expressed in this article are the author's own and do not necessarily reflect Al Jazeera's editorial policy.