For all the understandable excitement around Mario Draghi's and the European Central Bank's announcement, it's worth remembering that the euro won't be definitively saved or abandoned on Thursday. In all likelihood, we'll be talking about how much time has been bought for the eurozone to decide what it truly wants.
The answer will be "not much" if the central bank's bond-buying programme, known as the securities markets programme, is simply reheated in its old "temporary and limited" format. That would merely provoke a guessing game about how high Spanish and Italian bond yields will go when the ECB steps out of the ring. Similarly, another dose of LTRO (long-term refinancing operation) to allow Spanish and Italian banks to keep lending would look timid. The ECB has taken that path already and it hasn't stopped the economies falling into recession.
The launch of an unlimited bond-buying programme, with the aim of capping borrowing costs for member states, would better fit Draghi's pledge to do "whatever it takes" to save the euro. But investors would want to see it to believe it. For a start, they would want to know if the Bundesbank and German politicians agree with the tactic; until political approval has been seen to have been won, there's a credibility problem.
The same difficulty applies to the idea of giving the European stability mechanism (ESM) a banking licence, thereby increasing its firepower from the current level of €500bn. Draghi may feel such a manoeuvre would be sensible, and could even say so, but it's not in his gift to deliver. Only the politicians can turn the ESM into a bank since national balance sheets would be on the line as guarantors.
Still – if you're an optimist on the euro – it's a welcome development that Draghi even put himself at the centre of the stage with his comments last week. It must mean that he has something to say, or a wildcard to play. That's unless he says the market's interpretation was a "hilarious misunderstanding", as Dario Perkins of Lombard Street Research puts it. That would not be funny.