HHMT: The Romney economic program will change the direction of policy to focus on economic growth. Its pro-growth effects will work in two basic ways: It will speed up the recovery in the short run, and it will create stronger sustainable growth in the long run.That's just a small sample of a comprehensive and epic takedown, but I think that's the real point. Consider, as DeLong does, the effects of the Romney tax reform plan. The problem? There is no Romney tax reform plan. There are a set of mathematically incompatible claims -- what he'll do with tax rates and taxes on certain types of income; that it will be revenue-neutral; and that it will not affect the share of taxes paid by the rich and the middle class. We can't really know which of these promises will be broken by any real Romney plan, but one or more has to be just from the math of the tax code. Romney gets around the reality of this by keeping large chunks of that "plan" unspecified, but it just won't wash.
WRONG: There is no Romney program—a program is complete, coherent, and scoreable, Romney has repeatedly said that his statements are not scoreable. In order to estimate the economic effect of any program, you have to know what its pieces will do--you need to have it scored. Until Romney presents a complete and coherent program with scoreable pieces, HHMT have no basis for asserting anything about its economic impact.
One of the most annoying things here is the partisan asymmetry: the rules of the game seem to be that Democratic proposals have to be scoreable and coherent, while Republican proposals don't.
It would have been very nice if HHMT had done what we Democratic economists do--told their political masters that they could not estimate economic impacts until they were given a coherent, complete, and scoreable plan.
Why they did not do this I do not claim to know.
All of which gets back to my long-standing observation that there does seem to be a shortage of hack economists on the liberal side, which can also be interpreted as noting the presence of a lot of them on the conservative side.
For more on this sophisticated defense of Romney on taxes, see Matt Yglesias; for a nice takedown of a, shall we say, less sophisticated argument, Jonathan Chait has it covered. And: great catch!