Nate Silver from his FiveThirtyEight blog at the NYT:
“Although many of the surveys that are influencing the forecast preceded the debate, meaning that it will take another day or two before we can close the book on its effects, at the very least it seems clear that Mr. Obama will not see anything like the sharp break toward Mr. Romney that followed the first debate in Denver.
“A gain of two or three points for Mr. Obama in the polls, for instance, would very probably have become obvious by now. Perhaps the debate was worth a half a point or a full point for Mr. Obama — these trends would be more difficult to distinguish from statistical noise — but it probably wasn’t worth much more than that.” Emphasis added.
With the economy still as weak as it is, the bottom line is that O couldn’t afford a bad debate performance. It’s easier to slip than to climb back.