By default (or, rather, a series of near defaults), the president of the European Central Bank is fast becoming the most powerful person in Europe. Mario Draghi, who relieves Jean-Claude Trichet at the ECB as the euro zone’s top banker in November, proved at Italy’s central bank and Treasury that he has two qualities essential to running a central bank with one currency and 17 countries, five or more of them problem debtors: flexibility and temerity.

In August, Trichet and Draghi, acting as Italy’s central bank chief, sent Italian Prime Minister Silvio Berlusconi a letter stating that the ECB would help Rome by buying stressed Italian sovereign bonds — exhibiting flexibility, while reversing a dangerous spike in bond yields. At the same time, Draghi displayed temerity by endorsing the ECB’s demand that Italy meet stringent fiscal conditions that included balancing its budget a year ahead of schedule. Even cheekier, the joint missive proposed that Italy privatize utilities and cut public sector wages and pensions.....