For RealClearPolitics, Jeffrey H. Anderson looks at all examples since World War II of people trying to be elected president after a member of their own party has held the White House for eight years.
Anderson finds the best predictor of such candidate's success or failure is his predecessor's popularity in year six. Another decent predictor is to take the predecessor's reelection margin and deduct 9 percentage points.
By either measure, a Democrat is unlikely to be elected president in 2016. See the article for details. Normally Americans prefer to "throw the rascals out" every eight years (if not sooner) to give the other guys a chance.
Exceptions occur when the incumbent is very popular. Obama is not popular.
