The Tory mayoral candidate, Boris Johnson, was announcing a wheeze. He would remove free bus passes from unruly children but they could “earn” them back through community service. Ken Livingstone, his Labour opponent, stepped to the podium to reply and declared it a great idea that he would steal. Johnson sat dumbfounded, his mouth open. “But what sort of idiot wouldn’t steal a good idea when they heard it,” said the mischievous Livingstone. The people of London have been treated to three months of this sort of Clinton versus Obama backchat, with policies hurled back and forth and personalities stripped...