An oft-cited statistic is that, in five of the six post-World-War-II elections that took place after one party had held the White House for eight consecutive years, or two terms, the party defending the presidency lost. The only election that deviated from this pattern was in 1988, when Vice President George H.W. Bush was able to add a term onto that of his boss, Ronald Reagan. This suggests that the default setting is that after eight years of one party, Americans are generally receptive to change and ready to give the other side a turn. Or perhaps it’s that the grievances accumulated against a party over two terms make it very difficult for its nominee to retain the White House. Clearly, whether the sitting president is popular, or politically radioactive, matters.
In short, this history gives Republicans the advantage for 2016, unless Obama’s numbers are quite strong. Obama’s name will not be on the ballot next year, but how well or how poorly he is doing matters, and will help determine whether this pattern holds or whether it subsides.