His politics are that of principled rebellion. Between 2005 and 2010, when Labour was in government, Corbyn voted against party lines 25% of the time. Known for his anti-war politics, he has publicly supported both the Palestine Solidarity Campaign and Irish republicans. In 1996 the Guardian editorialized that his ill-timed meeting with Gerry Adams of Sinn Fein made him “a fool whom the Labour Party would probably be better off without.” Now, with the party in disarray, Corbyn has come out of obscurity to become Labour’s next leader — and British Jewry is worried. In a recent Survation poll, 67%...