The short answer is: because he’s got nothing. There is no record to run on, no argument to make for four more years. The ideology that drives him is outdated and bankrupt. He has, in fact, implemented his policies – Republicans have had little means of stopping him – and those policies are the problem.
But there’s a slightly longer answer too. Obama’s advisors will read the mainstream media assessment of the vice-presidential debate – they actually think a debate that turned women across America off of Biden was a draw, or a Biden win – and conclude that what the president needs to do is find his inner Joe Biden. Appeal to his base by going on the attack, perhaps interrupting, being visibly annoyed at the trend of Romney’s statements, andvigorously asserting untruths in the interest of racking up effective soundbites.
Petulant attack-doggery isn’t Obama’s style, so I don’t predict that he will simply adopt the Biden posture for this week’s debate. What I do think is that Obama and his handlers will be looking to enhance the president’s trademark pace and balance in public speaking (which does descend rather often into a sonorous drone) with more Biden-like spice. This won’t come naturally to Obama, any more than his occasionally put-on “black accent”sounds natural. It’s not who he is, and he won’t be good at it.
Of course, the townhall format this week can be worked to Obama’s advantage, and no doubt will be. Obama need not be thrown softballs, but he will get questions framed to suit the answers he is likely to have – and he probably won’t be troubled much with questions framed in a confrontational manner.
Romney probably will be. He will have to think more quickly on his feet, turning hostile questions into jumping-off points for getting his message across, while conveying a sense of goodwill and avoiding red herrings. If there is a “silly question” for the debaters – say, “If you were an Oscar-winning movie, which one would you be?” – it may well be barbed with false implications about conservatism, Republicans, or even Romney himself.