I don’t know if Barack Obama is a student of game theory, but his campaign pursued that strategy throughout. He doesn’t hit at his opponent until they have hit him, but once he’s been hit, his campaign always hits back.
Update: Here’s Barack Obama speaking on this subject:
One of the things we’ve done during this campaign: we don’t throw the first punch, but we’ll throw the last. Because if the American people don’t get the information that is relevant about these candidates and, instead, in the last four weeks, all they are hearing about are smears and Swift Boat tactics, that can have an impact on the election. We have seen it before, and this election is too important to be sitting on the sidelines. If Sen. McCain wants to focus on the issues, then that is what we focus on. But if Sen. McCain wants to have a character debate, that is one that we’re willing to have.