Nate Silver answers a question I've had for a while

From Nate Silver's analysis of Ryan's selection as VP (emphasis added)

The economy? Well, it isn’t very good. But it also doesn’t appear to be getting much worse, and some recent signs — like the July jobs report — suggest a slight brightening of the outlook. It’s not quite the case that incumbent presidents are favored to win unless there is an outright recession, but that also isn’t that far from the truth. Incumbent presidents tend to get the benefit of the doubt from voters, especially when, as in Mr. Obama’s case, they are regarded as likable, their party is in its first elected term, they are perceived as competent on foreign affairs and they have avoided major scandals.

I'd noticed that while assessments of political history often talked about a one-term president, I didn't hear much about how long a party held the White House. which always struck me as an important potential factor in a model. It's good (though hardly surprising) that Silver is considering it, but I do have to wonder how many of the experts on CNN are being as thorough.