I read John Taylor's response to Krugman, and found it pretty feeble and limited. But how would these guys actually defend themselves publicly, if they faced no political constraints?
From conversations I've had with people other than HHMT themselves, I suspect that they believe that a Romney Administration would end up following a set of unannounced policies (some, to a degree, hinted at) that are political poison, but that they believe Republican Party discipline would enable them to push through. An example is quite dramatic scaling back of the home mortgage interest deduction and employer-provided health insurance exclusion. People on the left keep saying: Because these things are political poison, and because you dare not even more than hint at them now, we know that they will never end up being passed.
But conservative economists for Romney may sincerely believe that this seemingly well-founded skepticism is incorrect. Again, if the Republicans have House and Senate majorities, and if they act like a purely parliamentary party led out of the White House, and if they use the tools at hand to squelch any Senate filibuster, then they can pass whatever they like in January 2013. Perhaps they even think that they would be able to replace the income tax with a consumption tax (!!). Then it's almost 2 years to the next election, and if the economy improves in the natural course of things they can take the credit (whether rightly or wrongly) and cruise on forward from there.
I don't agree that this would actually happen. While the Republicans will indeed, if placed in this position, make damn sure that the filibuster doesn't cause them any difficulties, I don't think they'll take White House direction. Nor would even a Romney White House be willing to attack politically popular tax preferences as much as the economists might hope (and perhaps have been told) that it would. So I would expect Medicaid cuts, budget-busting tax rate cuts at the top, and perhaps deferred tax preference cutbacks that will never end up taking effect as more than minor nicks.
Of course, even if a Romney White House did what the more principled conservative economists may expect and hope, the TPC study's critique would remain on point, since it is straight arithmetic. So the result would be a huge upward after-tax-and-transfers wealth transfer, privately rationalized by the more sincerely policy-minded on the belief that, within 10 years, a riding tide would lift all boats, plus on the view that accidents of the business cycle will permit them to take long-term control of the policy process, public opinion on particular issues notwithstanding.