A new Pew poll out today features some interesting numbers. The horse race number shows Barack Obama with a narrow four-point lead, a bit higher than the national average. But Mitt Romney does well on the economy:

The current survey finds that views of national economic conditions remain abysmal. Perhaps more important, the percentage saying they expect conditions to improve over the next year has fallen 10 points, from 44% to 34%, since March.

The slide in economic optimism points to Romney’s most important advantage in the race. Nearly half of registered voters (49%) say Romney would do the best job of improving economic conditions, compared with 41% who favor Obama.

This mostly confirms the basic dynamic of the contest. Mitt Romney functions as a generic Republican. Certainly on the economy, voters are accepting that his credentials seem to be sufficient.

In this poll, Obama tends to do best in personal traits — not only are his favorable ratings much higher, but he holds the edge in such things as “honest and truthful” and “good judgment in a crisis.”

The basic outline in the Pew poll is that this is a campaign in which more than enough swing voters like Obama and recognize that his presidency began with the nation in terrible shape…but they’re also unhappy with the progress made on the economy, and while they’re not looking to get rid of him, they aren’t particularly afraid of Romney, either.

Democrats might complain that it’s unfair that Romney has apparently cleared a basic threshold of competence on the economy; after all, he doesn’t exactly have detailed plans to respond to where we are now, and his private-business experience isn’t really especially relevant to the job of president. And it’s true that the Obama campaign might nudge the dial just a bit by attacking him on Bain and his record in Massachusetts.

Nevertheless, Obama advisers likely ecognize that there’s not very much they can do about the fact that Romney has cleared that threshold. He’s a generic Republican. Odds are that the places he’ll be vulnerable will have a lot more to do with the “Republican” part of that (such as his support for the House Republican budget, for example) than with any attempt to convince voters that he can’t be trusted on the economy.

The real way for Obama to win is to find ways to keep his own approval rating a bit higher than it is now. Romney has passed the threshold of acceptability as an alternative, and swing voters may turn to him if the economy is slow enough that they are ready to move on. The best way to prevent that is for Obama to do anything he can to boost the economy in the next few months. If he does, his approval rating will rise with it. Ultimately, his numbers matter more than Romney’s do, and it’s unlikely much can be done to change that.