Wilson Perkins Allen Opinion Research (WPA) has a very interesting analysis of Obama's polling numbers. When it comes to judging how Obama's approval ratings predict his reelction chances, WPA describes issue this way:
Is Obama in deep trouble facing an electorate where fewer than two-in-five voters think he’s doing a good job?
Or is in relatively good shape facing an electorate where most voters still like him personally?
There's a lot of actual analysis and number crunching at the link, so be sure and read the whole thing. But in a nutshell there's two big takeaways here:
While concepts like the trend line and the predictive power of job approval are interesting, sometimes the simplest analysis is the most valuable.
In this case, the result is simple and clear: exactly one President in the past ten who faced Election Day with a job approval below 50% was re-elected—Harry S. Truman in 1948.
As for personal approval:
Personal Approval ratings aren’t as clearly correlated with electoral success as are job approval ratings.
The President with the single highest personal approval ratings in our data set—Gerald Ford—failed to win on Election Day.
WPA wisely notes that a lot about Obama's numbers can change between now and election day, so it's far too early to suggest Obama's a one-termer. But it doesn't bode well.