Here's the conundrum at the heart of Romney's tax plan: He wants to lower tax rates by 20 percent, bringing the top tax rate down to 28 percent, but he doesn't want to increase the deficit or cut taxes on the rich. The problem is, the numbers don't add up, as both the Tax Policy Center and Harvard economist Martin Feldstein have demonstrated: Either Romney's plan will have to set rates higher than he's proposing, or the deficit will have to increase. 

On Monday afternoon, Romney adviser Kevin Hassett denied that his plan was mathematically impossible in a discussion with Obama economic adviser Jeffrey Liebman. But Hassett suggested that if Romney's plan proved impossible, or too difficult to get through Congress, Romney would choose to make his tax cut smaller rather than increase the deficit or put the burden on poor Americans:

If you think the base-broadeners don't add up, if you think he can't get to 28 percent, then the right thing that would happen, as you know, if you're going to have a revenue-neutral reform, is that they would have a different change in rates. 

Governor Romney says he can get to 28 percent. He believes he can get to 28 percent. When he's in office, he'll try to do it. But if Congress won't give him the base-broadening he needs to get to 28 percent, there's no way in hell that anyone believes that he's going to increase taxes by $2,000 on people with incomes below $20,000. I just can't believe that the Obama campaign would say that, and that an economist for the Obama campaign would be up here repeating these stupid and inane talking points.

In other words, according to Hassett, the public should assume that if Romney wants to make his tax plan work—should it prove politically or substantively impossible to implement reform as his campaign has laid out—we should assume that he would make the top rate higher than 28 percent to make the numbers add up. 

Romney hasn't said as much himself. But he has admitted more indirectly that he would need to raise taxes on the middle-class to make his own plan work.