Readers depressed at the state of U.S. politics can console themselves with the knowledge that however bad off their party might be, it’s not Britain’s Labour. The party of Clement Atlee, Harold Wilson, and Tony Blair now finds itself in the worst crisis in its 116-year history. It has not won a general election for a decade. Its advocacy of mass immigration and the European Union has alienated it from much of its voter base. And worse, it has lost whatever halo-advantage it once had by becoming irrevocably tainted with what was once one of the greatest sins of European civilization. Over the last 15 years, it became increasingly clear that anti-Semitism, which had previously been expected to surface only on the political right in Britain, had traveled around the political circle and snuck up behind the political left.