Mitt Romney on Thursday evening presented a politically effective argument: President Obama raised your hopes, only to dash them.

I don’t agree with that line of argument. Saving the country from economic catastrophe, laying the groundwork for a clean energy future, and making health care affordable for nearly all Americans represent a huge set of accomplishments—particularly given the obstacles, economic and political, that Obama faced from the day he took office. But with the unemployment rate still over 8 percent and the economy still growing too slowly, I’m sure Romney’s appeal will resonate with a lot of people.

But if you’re going to criticize the incumbent for the present state of the economy, you really should have a plausible plan for fixing it and doing so quickly. Romney doesn’t have one of those. And it showed in Thursday’s speech.

The first two-thirds of the speech played on emotion: Romney talked about America, his own life, and his (professed) disappointment that Obama didn’t succeed. Then he turned to policy—and devoted all of 200 words to his economic plan, at least by my count. I don't think the passage lasted more than three minutes. It certainly didn’t contain a lot of detail. It was, instead, a recitation of Romney’s five-point plan—a mix of nonsense proposals, like making North America energy independent, plus sweeping but unspecific promises to reduce the deficit, reduce taxes and reduce regulations.

Convention acceptance speeches don’t have to be wonky. Nominees use these speeches primarily to introduce themselves to the voters and to lay out the broad themes of what they hope will be their presidencies. But, in this case, the lack of specificity is of a piece with Romney’s whole campaign.