When Congresswoman Ilhan Omar posted a tweet denounced by fellow Democrats as anti-Semitic, one self-styled “Jewish” group rallied to her defense and organized a social-media campaign, #IStandWithIlhan. 

When Britain’s three Jewish newspapers published an unprecedented joint front-page editorial warning that the Labour Party under Jeremy Corbyn harbored anti-Semitism and constituted a threat to the Jewish community, one American “Jewish” organization issued a spirited defense of Corbyn, charging that “antisemitism is being cynically exploited to target advocates of Palestinian rights.”