The Obama campaign is not letting the issue of Mitt Romney's tax returns go away. It's calling on him to release more than just the two years of tax returns he's promised. And it's not just the Obama campaign — some Republicans have also called on Romney to release more. Romney points to the precedent of John McCain, who also released just two years of tax returns. To find out more about the precedent, Audie Cornish talks to Molly Ball, who covers politics for The Atlantic.