Meanwhile, there will likely be mounting pressure to do something about the brutal war of repression being waged by Bashar al-Assad in Syria. It is hard to imagine what that “something” might be; an intervention robust enough to make a difference would have more in common with the all-out Iraq invasion than with the more limited Libya campaign. But an atrocity can change attitudes overnight.

There’s also the possibility of an Israeli attack on Iran’s nuclear facilities. It may not happen — but if it does, there’s plenty of political danger here for both campaigns.

And if the Carville dictum turns out to be right? Well, stock markets around the world swooned on Monday — not because of anything U.S. officials said or did but because of events in Europe that made investors nervous. The Dutch government fell, after failing to win approval of new austerity measures, while French President Nicolas Sarkozy finished second in his bid for reelection and faces a runoff.

It may be that in 2012 it’s the euro-zone crisis, stupid. And there’s nothing Obama or Romney can do about it.