What they mean to say is “Gentile ethnic nationalism is bad for the Jews.”
That Trump’s efforts to mobilize white nationalism as a force in American politics has inadvertently also mobilized anti-Semitism does not come as a surprise to either white nationalists or Jews.
Jews have historically fared very well in the United States versus in other Western countries, in part because the United States — for all its deeply troubled racial history — has generally not defined American identity in ethnic blood and soil terms.
Organizations like the Ku Klux Klan that have wanted to bring more of that spirit to American politics have not looked kindly on the Jewish presence in American life. At the same time, even though Jews have never been subject to formalized legal discrimination in America, Jewish people were massively overrepresented in the ranks of white supporters of the civil rights movement — recognizing a shared interest in promoting an American civic identity and strong culture of nondiscrimination.
The idea of an ethnically conscious political mobilization of white people that garners heavy Jewish support makes a certain amount of sense in the specific context of late-20th-century New York City where Trump comes from. David Dinkins, the city’s first (and so far only) African-American mayor, defeated the Jewish incumbent mayor in the 1989 primary. Dinkins’s Republican opponent, Rudy Giuliani, lost narrowly in 1989 and won narrowly in 1993, both times securing many Jewish votes. But these electoral dynamics are entirely disconnected from the larger logic of American politics in a way that Trump’s Jew-bashing supporters see quite clearly even if Trump himself does not.
Meanwhile, Trump has not acted to distance himself in any way from the anti-Semitic behavior of his followers. There’s been nothing remotely in the vicinity of Barack Obama’s famous race speech from the 2008 campaign, and Trump has consistently appeared angrier about being criticized for ties to anti-Semites than about the anti-Semitism expressed by many of his fans. His campaign is promoting ethnic nationalism in a way that hasn’t been seen in decades, and that mobilization of majoritarian ethnic identity is bad for the Jews, whether Trump likes it or not.
