More and more mainstream outlets are pointing out that they fail to validate its soundness. And on Sunday Romney senior adviser Ed Gillespie was challenged on Fox News by Chris Wallace, who questioned whether the studies are really nonpartisan.
"Those are very questionable. Some of them are blogs. Some of them are from the AEI [American Enterprise Institute], which is hardly an independent group," Wallace said. "One of them is from a guy who is -- a blog from a guy who was a top adviser to George W. Bush. These are hardly nonpartisan studies."
"These are very credible sources," Gillespie said.
Of the six studies, two are blog posts by the conservative American Enterprise Institute; one is a report by the Republican-friendly Heritage Foundation; one is a paper by Princeton professor and former George W. Bush adviser Harvey Rosen; the fifth and sixth are a Wall Street Journal op-ed and blog post by Harvard economist Martin Feldstein, an adviser to the Romney campaign.
In addition, not all the studies appear to reach the same conclusion as Romney. He contends they show that it's possible to lower tax rates across the board by 20 percent and avoid adding to the deficit by unwinding deductions and credits for high incomes. That's not the case.
Feldstein, for instance, concludes that the numbers add up if effective taxes rise on incomes between $100,000 and $200,000, even though Romney has ruled that out. Rosen, for his part, makes the math work by omitting part of the revenue losses and assuming huge economic growth effects from tax reform.
Months ago, Romney's proposal was called into question by the nonpartisan Tax Policy Center, which found that even under friendly assumptions, there aren't enough loopholes in the tax code for incomes above $200,000 to make up for his nearly $5 trillion in tax cuts. In other words, the plan would either force the middle class to pay more or increase the deficit.
The other studies that Romney cites -- the two blog posts by AEI and the report by Heritage -- question the contours of the TPC paper or posit different revenue baselines. Neither of them comprehensively illustrate how the GOP nominee's math might add up.