Howard Gleckman tries to make sense of it:
Romney’s promise to make his new system as progressive as today’s puts him in a difficult policy box. Which tax preferences aimed at upper-income households could he dump to keep the code progressive while not adding hundreds of billions to the deficit?
Raising rates on capital gains and dividends might help, but he’s already promised to cut them to zero for those making $200,000 or less and hold them at 15 percent for everyone else. Eliminating or restructuring tax breaks for retirement savings, mortgage interest, and employer-sponsored health insurance could make Romney’s low-rate system more progressive, but these changes would be hugely controversial.