Obama continues to insist that Romney has proposed a $5 trillion tax cut -- he did it again today at a rally in Denver -- and liberal commentators such as Greg Sargent and Steve Benen make the same claim. But that line of attack is too rigid. Romney can wriggle out from under it, as he did during the debate (as I forecast a half hour prior).
It remains true, deny though Romney will, that he cannot a) cut marginal rates by 20%, b) make that cut revenue neutral by reducing tax deductions, c) exclude investment income from the deduction reduction, and d) not raise taxes on Americans earning less than $200k per year. It's also true that Romney has promised to do all of the above. Romney, therefore, is lying.
But it's not true that Romney has proposed a $5 trillion tax cut (over 10 years). He's proposed a $5 trillion marginal rate cut. That means he must either a) increase the structural deficit by up to $5 trillion by failing to reduce deductions enough to offset the rate cut (i.e., cut taxes by up to $5 trillion); b) raise taxes on the middle class; or c) not cut marginal rates by a full 20% across the board. Recently, he's intimated that he will break his package promise by going for option c). You may argue, as Jonathan Bernstein and others have done, that the likeliest option is massive rate cuts with only token, or at least wildly inadequate, loophole closures. But that's an inference -- choosing one of three doors. You can also point out that in past debates Romney has referred to his "tax cut." But he can plausibly claim to have misspoken -- from the beginning, he's included the not-credible "revenue neutral" claim.
It's hard to attack incompatible promises in a sound byte, especially four-part promises. But insisting that Romney proposes to "cut taxes" by $5 trillion simply affords him deniability.
Romney's contortionist abilities should come as a surprise to no one. They were on full display throughout primary season, when he proved himself the best liar in the field and soothed appearances of inconsistency with a multi-verse lullaby.