The problem here is that ACA is entitlement reform.
As Yglesias points out, the main reason that Obama hasn't done more deficit-cutting is because the Republican Party is opposed to it:
The filibuster rule and the Democrats’ reluctance to push the health care bill through with reconciliation gave them a ton of leverage over the process. It was leverage that they, or any subset of them, could have used at any time to try to secure more robust deficit reduction measures. But they chose, individually and collectively, not to use that leverage in that way.Read the whole post; it's very good. I suppose I should add to this three things. One is that deficit reduction is almost always popular in the abstract but very unpopular whenever it's attached to specific tax increases or spending cuts. The second is that not only did Republicans oppose deficit reduction within Congress, but while ACA was being debated virtually all of their attacks on ACA were precisely against the "entitlements reform" portions of it: the cuts to Medicare Advantage, and the establishment of new cost controls on Medicare. That was true of GOP 2010 campaigns as well, which highlighted "Medicare cuts."
And the third thing, the one that's very much reflected in Douthat's column, is that for whatever reason prominent deficit hawks have basically given Obama no credit at all for the deficit reduction in ACA. The truth is that by normal standards, the choice by Barack Obama to fight hard for deficit-reducing health care reform, when it was not apt to do him a bit of good, was actually one of the more "responsible" acts of presidential leadership I can think of. He almost certainly would have been far better off in terms of short-term politics fighting for irresponsible health care reform (assuming that it could have passed; it's hard to know if that was possible or not). He obviously won zero GOP votes in Congress by being "responsible" in terms of long-run deficits, and I'm confident that attacks on the basis of budget-busting would have been no more, and almost certainly less, effective than attacks over cutting Medicare and death panels. But none of that yielding the support from the (sincere) deficit idealists that it should have received.