The hatred looks different this time. There are no ghettos or pogroms; no European government espouses it. In some ways the recent surge of antisemitism—including the stabbing of two Jewish men in London on April 29th—has a distinctly 21st-century character. Stand back, though, and the mindset of prejudice is horribly familiar. So are the risks: for Jews across the diaspora, but not only for Jews.The hatred looks different this time.The bloodshed in Golders Green, a hub of Britain’s small Jewish community, followed a spate of firebombings at Jewish sites in London. Last October an attack on a synagogue in Manchester...