The European Central Bank has opened the door to a blitz of bond purchases and fully-fledged quantitative easing in a radical shift of policy, but only once Europe’s leaders have activated their own rescue machinery. Mario Draghi, the ECB’s president, said the bank may “undertake outright open market operations” to cap borrowing costs in those countries pushing through reforms. Intervention will be of “adequate size” to fulfil the task. “These are very strong words,” said Julian Callow from Barclays Capital. “Draghi has made it clear that the ECB is preparing to buy Spanish and Italian bonds on a much bigger...