It's sometimes said that the most optimistic presidential candidate is inevitably the one who wins. If that's true, Barack Obama is a shoe-in, considering what he said on Friday about the "fever" of Republican intransigence. "I believe that if we're successful in this election," the President mused, "that the fever may break, because there's a tradition in the Republican Party of more common sense than that. My hope, my expectation, is that after the election, now that it turns out that the goal of beating Obama doesn't make sense because I'm not running again, that we can start getting some cooperation again." And if you believe that, I've got some mortgage-backed securities you might be interested in.
But Obama doesn't have much choice. He can't exactly come out and say, "If I'm re-elected, it'll be pretty much the same excruciating, maddening, ridiculous partisan thunderdome we had in my first term, with every accomplishment coming only at the tail end of a horrific legislative nightmare, punctuated by periodic Republican attempts to hold the economy hostage." That, unfortunately, is pretty much what it will be. But he has to offer some vision that things will improve on that score, and the only way he can do so is to argue that his re-election will convince Republicans to improve their behavior. After all, he can't say that he'll reach out to them and that will get results, since we just went through three and a half years of that. So it's on them.
Since Obama has been president for a while, he can't go back to the gauzy, "vote-for-me-and-America-will-become-a-paradise" rhetoric that is the privilege of every challenger. Mitt Romney can say that, because his presidency is entirely theoretical at this point. Republicans (and many in the media) have been criticizing Obama of late because his 2008 campaign was all about hope, and his current campaign isn't quite so high-minded and poetic. But if he came out and gave the same speeches he did four years ago, it would sound ridiculous. He's the incumbent, and incumbents just can't do that. Their presidencies exist in the real world, not in our imaginations, and the real world is grubby and often unpleasant. There isn't much way around it.
See Matthew Zeitlin for more on this.