The problem for the President is that his window of opportunity to demonize Romney is quickly closing. Given the disaster his own policies have been, it's impossible to frighten Americans about the policies that Romney would ostensibly pursue; therefore, the President instead has been trying to disqualify Romney on a personal level (but given the disaster the Obama years have been, it's far from clear that anyone will care).
Soon, the conventions will be upon us. Voters will have the chance to see Romney for themselves, and the topic of his veep choice will provide fodder for the media. Could it be that the President is squandering his last, best chance to lock the race up?