JUST a few months ago the euro zone’s leaders believed that, having weathered the storm, they were set fair at last. Buoyed by the promise of Mario Draghi, the president of the European Central Bank, to do “whatever it takes” to support the currency, confidence had seeped back into the continent. Growth seemed to be returning, albeit at a slow pace. Troubled peripheral countries were recovering, after bail-outs and painful measures to cut budget deficits and improve competitiveness. Unemployment, especially among the young, was still desperately high, but at least in most countries it was falling. And bond spreads had narrowed sharply, as financial markets stopped betting that the euro would fall apart.