Obama and Romney are tangling over views of Romney's tax proposal. The nonpartisan Tax Policy Center has analyzed the specifics thus far released from Romney's plan and concluded the numbers aren't there to make it revenue neutral.

Obama, in referring to Romney's plan as a $5 trillion tax cut, is basing that on the estimate of reducing tax rates by 20 percent while also extending the Bush tax cuts, two planks of the plan. Romney has argued that he can eliminate loopholes and deductions to make up that revenue but has not specified which ones. 

Romney has countered that "six other studies" have found that the plan can be revenue neutral, but he's wrong about that. Those studies actually do not provide much evidence that Romney's proposal -- as sketchy as it is -- would be revenue neutral without making unrealistic assumptions.