Prompted by Nate Silver’s latest thoughts on this topic, Ezra Klein asks, “Do Speeches Work?” His conclusion:

That said, the polls measure public opinion. The speech’s impact on elite opinion is rather different. My sense from reporting in the past week is that it really did invigorate the players on the Democratic side, if only by providing a clean break with the dispiriting hysteria of August. The speech created space for the legislative process to restart, which was pretty much what it needed.

Sounds like he subscribes to the it’s-not-about-(or least not all about)-the-polls theory.