In a recent spate of hate crime attacks on Hasidic Jews in Crown Heights, Brooklyn, virtually all the perpetrators have been African-American, according to local activists, elected officials, and victims. Yet at a recent news briefing reporting an 82 percent increase in anti-Semitic incidents in the city, when New York City Mayor Bill de Blasio was asked about the attacks, he connected the attacks to national trends, blaming “white supremacy” and “nativism.” “It’s really clear that forces of white supremacy have been unleashed,” de Blasio said in a press conference earlier this month. “A lot of folks used to be...