Political turmoil and talk of Italy leaving the single currency sparked a surge in its government bond yields. Other southern European countries, such as Portugal and Spain, also suffered some contagion.
Two-year Italian debt was yielding as much as 2.73 percent on Tuesday, compared with sub-zero levels less than a fortnight earlier. Investors have since calmed down but, as Italian central bank chief Ignazio Visco pointed out this week, his country risks losing "the irreplaceable asset of trust".
Were this to happen, the ECB has a few options. It could ditch plans to wind down bond purchases, and instead buy more assets for longer. It can also directly support a single country through the Outright Monetary Transactions (OMT) programme, unveiled in 2012, which in theory allows the central bank to buy short-term bonds in unlimited quantities. On paper, it has the firepower: relative to GDP, the ECB's balance sheet is less than half as big as the Bank of Japan's.
However, it's hard to imagine a radical Italian government accepting the strict economic policy prescriptions that any OMT programme would involve. And it would be almost impossible for the ECB to help an explicitly eurosceptic administration.
During the first iteration of the euro zone crisis, policymakers worked hard to stop contagion from smaller southern European countries from infecting Italy, the euro zone's third biggest economy, which was considered too big to bail out. Now the contagion is emanating from Italy itself.
If an Italian government blatantly flouted the EU's rules, Germany and others might prefer to erect a firewall around the rest of the euro zone and leave Italy to the mercy of markets. In that scenario Draghi might be more use to his country in Rome than in Frankfurt.
The 70-year-old, who is due to leave the ECB in October next year, is the sort of technocrat who is reviled by radicals. But he is also one of the few Italians who could win back the trust of the markets.