Editor's note: Ian Buruma is the author, most recently, of "A Tokyo Romance: A Memoir". The article reflects the author's opinions and not necessarily the views of CGTN.

U.S. President Donald Trump thinks that anti-Semitism is a serious problem in America. But Trump is not so much concerned about neo-Nazis who scream that Jews and other minorities "will not replace us," for he thinks that many white supremacists are "very fine people."

No, Trump is more worried about U.S. college campuses, where students call for boycotts of Israel in support of the Palestinians.

Trump just signed an executive order requiring that federal money be withheld from educational institutions that fail to combat anti-Semitism. Since Jews are identified in this order as a discriminated group on the grounds of ethnic, racial, or national characteristics, an attack on Israel would be anti-Semitic by definition. This is indeed the position of Jared Kushner, Trump's Jewish son-in-law, who believes that "anti-Zionism is anti-Semitism."

There are, of course, as many forms of anti-Semitism as there are interpretations of what it means to be Jewish. When Trump and his supporters rant in campaign rallies about shadowy cabals of international financiers who undermine the interests of "ordinary, decent people," some might interpret that as a common anti-Semitic trope, especially when an image of George Soros is brandished to underline this message.

Trump even hinted at the possibility that the liberal Jewish human rights promoter and philanthropist was deliberately funding "caravans" of refugees and illegal aliens so that they could spread mayhem in the U.S. In Soros's native Hungary, attacks on him as a cosmopolitan enemy of the people are unmistakably anti-Semitic.

Conspiracy theories about sinister Jewish power have a long history. The Protocols of the Elders of Zion, a Russian forgery published in 1903, popularized the notion that Jewish bankers and financiers were secretly pulling the strings to dominate the world. Henry Ford was one of the more prominent people who believed this nonsense.

The history of extreme anti-Zionism is not so long. In the first years of the Jewish state, Israel was popular among many leftists, because it was built on socialist ideas. Left-wing opinion in Europe and the United States began to turn against Israel after the Six-Day War in 1967 when Arab territories were occupied by Israeli troops. More and more, Israel came to be seen as a colonial power, or an apartheid state.

One may or may not agree with that view of Israel. But few would deny that occupation, as is usually the case when civilians are under the thumb of a foreign military power, has led to oppression.

So, to be a strong advocate for Palestinian rights and a critic of Israeli policies, on college campuses or anywhere else, does not automatically make one an anti-Semite. But there are extreme forms of anti-Zionism that do. The question is when that line is crossed.

Some would claim that it is anti-Semitic to deny Jews the right to have their own homeland. This is indeed one of the premises of Trump's presidential order. There are also elements on the radical left, certainly represented in educational institutions, who are so obsessed by the oppression of Palestinians that they see Israel as the world’s greatest evil.

Just as anti-Semites in the past often linked Jews with the U.S., as the twin sources of rootless capitalist malevolence, some modern anti-Zionists combine their anti-Americanism with a loathing for Israel.

In the minds of certain leftists, Israel and its American big brother are not just the last bastions of racist Western imperialism. The idea of a hidden Jewish capitalist cabal can also enter left-wing demonology as readily as it infects the far right. This noxious prejudice has haunted the British Labour Party, something its leader, Jeremy Corbyn, has consistently failed to recognize.

In short, anti-Zionism can veer into anti-Semitism, but not all critics of Israel are anti-Zionist, and not all anti-Zionists are prejudiced against Jews.

Quite where people stand on this issue depends heavily on how they define a Jew – a source of endless vagueness and confusion. According to Halakha, or Jewish law, anyone with a Jewish mother, or who has converted to Judaism, is Jewish. That is the general Orthodox view. But more liberal Reform Jews allow Jewish identity to pass through the father as well.

On the other hand, while most Orthodox Jews consider a person to be Jewish even if they convert to another religion, Reform Jews do not. Israel's Law of Return grants "every Jew" the right to immigrate, but refrains from defining Jewishness. 

Since 1970, even people with one Jewish grandparent have been eligible to become Israeli citizens. In the infamous Nuremberg laws, promulgated by the Nazis in 1935, people with only one Jewish parent could retain German citizenship, while "full" Jews could not.

The whole thing is so complicated that Amos Oz, the Israeli novelist, once sought to simplify the matter as follows: "Who is a Jew? Everyone who is mad enough to call himself or herself a Jew, is a Jew."

There is, in any case, something ill-conceived about the stress on race and nationhood in Trump's order on combating anti-Semitism. Israel is the only state claiming to represent all Jews, but not all Jews necessarily identify with Israel. Some even actively dislike it.

Trump's order might suggest that such people are renegades, or even traitors. This idea might please Israel's current government, but it is far from the spirit of the Halakha, or even from the liberal idea of citizenship.

Defining Jews as a "race" is just as much of a problem. Jews come from many ethnic backgrounds: Yemenite, Ethiopian, Russian, Moroccan, and Swedish Jews are hard to pin down as a distinctive ethnic group. Hitler saw Jews as a race, but that is no reason to follow his example.

To combat racism, wherever it occurs, is a laudable aim. But singling out anti-Semitism in an executive order, especially when the concept is so intimately linked to views on the state of Israel, is a mistake. Extreme anti-Zionists may be a menace; all extremists are. But they should be tolerated, as long as their views are peacefully expressed.

To stifle opinions on campuses by threatening to withhold funds runs counter to the freedom of speech guaranteed by the U.S. Constitution. This is, alas, not the only sign that upholding the constitution is not the main basis of the current U.S. administration's claim to legitimacy.

Copyright: Project Syndicate, 2019.

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