Use the Weapons You Have
And to add to what Krugman says here in defense of using Romney’s Bain record against him, it’s worth noting that Republicans have come up with a great scam: the Ryan plan to gut Medicare in order to finance upper-class tax cuts is so “cartoonishly evil” that you literally can’t get voters to believe that Romney supports it. You can’t rely solely on policy arguments in a political campaign, and the business record he’s running on isn’t like discussing Romney’s suits or something.