One theory floated around about the swing state-national discrepancy is that Mitt Romney is doing a lot better in under polled red states. Sean Trende of Real Clear Politics pointed out on Twitter why this is unlikely.
John McCain maxed out White support in Alabama, Mississippi, and Louisiana, getting at least 85% of the vote. While Romney can improve his share of the White vote in other states, that's unlikely here. He probably came close to maxing his support in South Carolina, Texas, and Georgia. The only way for Romney to improve in these states is to grab support from Blacks, something he's unlikely to do. As our Democratic friends constantly remind us, the south is becoming less White each year. So it's unlikely we'll see much of an increase in the White electorate.
If you're looking for states for the President to improve in, Alabama, Mississippi, and Louisiana are probably good bets.