Key difference between Barack Obama and John McCain: Unlike his notoriously temperamental Republican opponent, Obama tends to keep his cool even in the most trying of circumstances. For communicating that message to voters, Obama's appearance on David Letterman last night was effective politics. The presidential nominee joked about the ginned-up scandal around his use of the phrase "lipstick on a pig," and that phrase's alleged ties to McCain running mate Sarah Palin. He even got in a clever wisecrack about being jealous of Palin's celebrity. The only snag is that Letterman's audience, at least compared to its competitors, tends toward the younger coastal "elites" who were already going to vote for Obama. Sigh. At least we'll always have the clip. Click the video icon to watch. [via Huffington Post]