If President Obama reaches a 50 percent approval rating by March, pollsters and experts say he may be in good shape for re-election. Since the middle of July, the weekly average of Obama's approval rating has been between 40 and 43 percent, according to Gallup. Historically, presidents' approval ratings haven't changed much during their re-election years. And at least before the parties' summer conventions, those ratings can fluctuate with less consequence, said Chris Wlezien, a political science professor at Temple who has analyzed the accuracy of polls leading up to elections.