It’s that time again: the annual meeting of the American Economic Association and affiliates, a sort of medieval fair that serves as a marketplace for bodies (newly minted Ph.D.’s in search of jobs), books and ideas. And this year, as in past meetings, there is one theme dominating discussion: the ongoing economic crisis.

This isn’t how things were supposed to be. If you had polled the economists attending this meeting three years ago, most of them would surely have predicted that by now we’d be talking about how the great slump ended, not why it still continues.

So what went wrong? The answer, mainly, is the triumph of bad ideas.

It’s tempting to argue that the economic failures of recent years prove that economists don’t have the answers. But the truth is actually worse: in reality, standard economics offered good answers, but political leaders – and all too many economists – chose to forget or ignore what they should have known.

The story, at this point, is fairly straightforward. The financial crisis led, through several channels, to a sharp fall in private spending: residential investment plunged as the housing bubble burst; consumers began saving more as the illusory wealth created by the bubble […]