As Michael Barone documents in his latest column, the Rust Belt counties of Ohio and Pennsylvania have voted consistently for Democratic presidential candidates, giving even Walter Mondale a substantial victory.

Now, though, the situation has changed.

The polling data suggests that Obama is not running as strong in the Rust Belt counties this year. The [recent two-day] bus tour was undoubtedly aimed at pushing his numbers up.

But he seems to have been left with little to say. No wonder he resorted to making jokes about his family and adding, “People’ve been commenting: I need to gain some weight.”

As if to compensate, he ate some grits — a staple once you get an hour or so south of Washington, but not so much up north.

But what else could he talk about? Certainly not the Environmental Protection Agency’s rules shutting down coal-fired electric plants. Nor his decision blocking the Keystone oil pipeline.

He could hail the development of fracking in the region’s Marcellus shale natural gas formation in the region, except for the fact that regulators in his administration seem intent on shutting it down.

He could repeat his calls for “investment” in education, but even if you don’t regard that as a political payoff to the teacher unions, the dividends are going to be a long time coming in.

And calls for investment in infrastructure may lead people to recall his chuckling admission that there are no shovel-ready projects, thanks to regulatory and legal roadblocks.

The uncomfortable fact is that Obama doesn’t have a convincing economic story to tell. The recovery summer promised for 2010 and for 2011 and again for 2012 has yet to arrive.