Romney's weakness when debating is that he comes across as nasty and is prone to gaffes when he responds to a pointed attack. Obama will go for him knowing this. He'll get pounded on Romneycare and his crap foreign policy credentials as well as all the Bain stuff. It'll be a bruising encounter.
Biden will just make Ryan look like an amateur.
Yeah that's how I read it as well. Obama's cool style makes his debating opponents come off as a bit desperate. Biden was also surprisingly good against Palin.