Obama was forceful, poised, presidential, blah blah blah blah. You can get that shit on TV.
Here's what really struck me: Obama's biggest weakness is the notion that he's not ready or experienced enough. It was the basis of many a McCain attack: "Senator Obama doesn't understand/doesn't get it..." He flat out accused Obama of not having the judgment to lead at one point.
Obama fought back by speaking at length on every issue, aided by a format that allowed him to speak beyond 30 second sound bites, and he name dropped countries and foreign leaders by the bucketful, to underscore the fact that he knows what he's talking about. It was very effective.
There were no gaffes, and no obvious YouTube moments, so if nothing else, this debate maybe reinforced Obama's fitness to be president, but I don't think that line of attack has had much salience beyond the wingnut sense anyway.
And given where McCain is in the polls (lagging and getting worse), this wasn't what he needed tonight.
And given that the status quo probably remains, in a debate that was supposed to focus more on McCain's "strength" (national security), Obama wins.
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One other point -- Lehrer was the best moderator, BY FAR, of any debate this season. And the audience was perfectly behaved. A triumphal debate. Perfect. Kudos to everyone involved in making it happen.