A study by the Tax Policy Center, a project of the center-left Brookings Institution and Urban Institute, claims that Mitt Romney's tax plan is mathematically impossible. TPC claims that Romney cannot cut tax rates by 20 percent across the board and maintain revenue neutrality without raising the net tax burden on the middle class. According to TPC, in the year 2015 under Romney's tax plan, "maintaining revenue neutrality mathematically necessitates a shift in the tax burden of at least $86 billion away from high-income taxpayers onto lower- and middle-income taxpayers. This is true even under the assumption that the maximum...