Nate Silver is skeptical of this concept:
What’s less clear is if there is any systematic tendency for a president’s approval ratings to decline in his second term, other factors held equal — like, for example, because the public is increasingly fatigued by having the same person in office. It is also hard to make very many generalizations from only seven data points, some of which reflect different circumstances than the ones that Mr. Obama now faces. (For instance, Mr. Truman and Mr. Johnson, who had among the largest declines in their approval ratings, were serving their first elected term in their second overall term.)
Silver’s theory:
My view, then, is that the idea of the second-term curse is sloppy as an analytical concept. There is certainly a historical tendency for presidents who earn a second term to become less popular — but some of this reflects reversion to the mean. And some recent presidents have overcome the supposed curse and actually become more popular on average during their second terms.
