Obama has released another set of NC/Indiana ads attacking Clinton for her proposal to suspend the gas tax. This is sharper, a bit more personal than either of his first two responses to her ads, which also attack him by name for not supporting the idea.
This is, indeed, the issue that has been joined for NC and Indiana. Traditionally, you want to be on Hillary's side of the money -- offering a tax break to the voters. It'll be a surprise if Obama's stance really helps him make inroads into her low-income white demographic. But maybe the plan is just to secure his "wine-track" share of the white and youth vote, by taking the "principled" stand approved by the ed boards: