As you'll recall, the 50 Percent Rule (a.k.a. the "incumbent rule") states "an incumbent who can't break 50 percent is in trouble."
Well, it seems Kerry pollster Mark Mehlman, writing in The Hill last Sunday, had a different interpretation: "We simply do not defeat an incumbent president in wartime. After wars surely, but never in their midst. Republicans have been spinning this fact for months, and they are correct."
Of course, the "incumbent rule" wasn't the only failure in this election. The exit polls failed terribly and, as Mystery Pollster notes, the haggling over likely voter models was misguided. They actually performed fairly well.