A spokesperson for Sen. Bernie Sanders, I-Vt., was forced to apologize on Tuesday for spreading the idea that Jews had dual-loyalty, thus demonstrating that liberal anti-Semitism is not confined to the utterances of Rep. Ilhan Omar, D-Minn.

In the wake over the dustup caused by Omar's remarks in which she lamented Jewish influence in politics which she said pushes people to declare their allegiance to a foreign government, many of her defenders argued her remarks didn't have anything to do with Jews, and that really she was just talking about the influence on pro-Israel lobbying, just as she would any other special interest group.

But Belen Sisa, Sanders’ national deputy press secretary, left no doubt that she was questioning Jewish loyalty.

In a Facebook thread, Sisa wrote, "This is a serious question: do you not think that the American government and American Jewish community has a dual allegiance to the state of Israel? I’m asking not to rule out the history of this issue, but in the context in which this was said by Ilhan.”

After Politico contacted Sisa about the comments, she apologized.

It is no surprise that Sanders, who has been one of Omar's most prominent defenders, would have somebody on his staff spreading anti-Semitism, as anti-Semitic views are becoming more and more common on the Left.

Liberals have become increasingly hostile to Israel, and while arguments against Israeli policies do not need to be polluted by anti-Semitism, such bigoted tropes often creep into the debate, and liberals then excuse them by trying to launder them as mere criticism of Israel.

Yet, like Omar, Sisa was not criticizing any specific Israeli policy. She was not arguing against the occupation, or policies in Gaza, or housing construction, or U.S. foreign aid, or even making an affirmative case for boycotting Israel until they change their policies. Instead, she was questioning whether Jews were loyal Americans.

The idea of Jews being disloyal to their old country is an age-old smear that has been used to justify centuries of persecution against the Jews, and dates back to well before the establishment of Israel. In fact, the development of Zionism in the first place was greatly influenced by the "dual loyalty" conspiracy theory.

In the late 19th century, there was a famous case, known as the Dryfus affair, in which a Jewish military officer in France was arrested and jailed after being falsely accused of spying for Germany, convicted with the use of forged evidence. One of the young reporters on the story, Theodor Herzl, was greatly influenced by the episode, as it convinced him of the need for a Jewish homeland. He ended up becoming a founding father of the modern Zionist movement.

Anti-Semitism has proven resilient because of the way it constantly morphs to changing circumstances. Israel was established so that Jews would finally have a place where they could live safely without their Judaism being used against them to question their loyalty to the nation. Now, the existence of Israel itself is being used to question Jewish loyalty in the rest of the world. And in the United States, because liberals are generally critical of Israel, even those who aren't themselves anti-Semitic, are allowing the old anti-Semitic canards to sneak their way into acceptable debate by santizing them as criticism of Israel. If this isn't stopped, it will have dangerous implications for American Jews, and by extension, for the United States.