So far, so good. But then, at the end of a post that began with a skeptical point of view, Cillizza gets a little credulous. Debates can matter when they “create windows of opportunity for underdog candidates to make up ground,” he writes, and singles out the October 2007 exchange in which Hillary Clinton stumbled over a question about whether illegal immigrants should get drivers licenses.

What seemed like an afterthought in a very contentious debate that centered on the Iraq war (among other weighty topics) wound up signaling the beginning of Clinton’s decline as the driver’s license equivocation came to symbolize everything voters disliked about her.

This might be true, but the evidence for it is pretty thin. The aggregate polling data for the 2008 Democratic primary shows that Clinton’s support was remarkably stable over a long period. This is really not surprising—she had been a national figure for a long time, and people had pretty settled opinions about her. It is the case that Obama’s support skyrocketed at about the time of that debate—but that’s probably a function of him consolidating support undecided voters who were already reluctant to back Clinton.

In other words, voters who didn’t back Clinton because of her “equivocation,” or for other factors, probably didn’t need any new symbols or signals. But journalists who had to update an old meme with some fresh news pegs did—and the debate stumble came in handy. As Stimson writes, after an election, we ask:

Why did the winner win? Why did the loser lose? It is tempting to use the debate to settle both questions, to find high moments that were good for the winner and lows that were bad for the loser.

But it’s at that point, he adds, that those much-maligned horse-race polls can be a corrective—because, they, “unlike the stories we tell after the fact, are not a social construction.”

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Greg Marx is a CJR staff writer. Follow him on Twitter @gregamarx.