Barry Eichengreen asks himself why his influential analysis, suggesting that the euro was irreversible now appears wrong. Surely in a direct, mechanical sense what we’re seeing is the process I warned about five years ago:

Think of it this way: the Greek government cannot announce a policy of leaving the euro — and I’m sure it has no intention of doing that. But at this point it’s all too easy to imagine a default on debt, triggering a crisis of confidence, which forces the government to impose a banking holiday — and at that point the logic of hanging on to the common currency come hell or high water becomes a lot less compelling.

But doesn’t the ultimate cause lie in wild irresponsibility on the part of the Greek government? I’ve been looking back at the numbers, readily available from the IMF, and what strikes me is how relatively mild Greek fiscal problems looked on the eve of crisis.

In 2007, Greece had public debt of slightly more than 100 percent of GDP — high, but not out of line with levels that many countries including, for example, the UK have carried for decades and even generations at a stretch. It had a budget deficit of about 7 percent of GDP. If we think that normal times involve 2 percent growth and 2 percent inflation, a deficit of 4 percent of GDP would be consistent with a stable debt/GDP ratio; so the fiscal gap was around 3 points, not trivial but hardly something that should have been impossible to close.

Now, the IMF says that the structural deficit was much larger — but this reflects its estimate that the Greek economy was operating 10 percent above capacity, which I don’t believe for a minute. (The problem here is the way standard methods for estimating potential output cause any large slump to propagate back into a reinterpretation of history, interpreting the past as an unsustainable boom.)

So yes, Greece was overspending, but not by all that much. It was over indebted, but again not by all that much. How did this turn into a catastrophe that among other things saw debt soar to 170 percent of GDP despite savage austerity?

The euro straitjacket, plus inadequately expansionary monetary policy within the eurozone, are the obvious culprits. But that, surely, is the deep question here. If Europe as currently organized can turn medium-sized fiscal failings into this kind of nightmare, the system is fundamentally unworkable.