Mulling Obama’s tax deal with the Republicans, and the circumstances that led to it, I keep coming back to that very telling moment in last week’s presidential press conference—the part where Obama responded to liberal critics angry at him for giving so much ground.

The essential problem with liberal critics, Obama suggested, was that they were “purists” more interested in symbolism than progress—that, in effect, they were letting the perfect be the enemy of the good. It was, Obama continued, the same thing he’d seen and heard during the health care reform debate, when critics on the left became ambivalent about or downright hostile to the Affordable Care Act because it didn’t have a public insurance option.

That analogy to health care resonated with me; as readers of this space know, I’ve made that very same point many, many times. I’m a strong proponent of the public option and continue to believe that reform with a public option would be much better than reform without it. But I also think the Affordable Care Act, as written, will do a lot of good. That’s why I think it’s worth supporting—and why, like Obama, I think it will go down as a great historical victory alongside the creation of Social Security and Medicare.

But I don’t think it’s fair to make the same argument about the tax deal.

The Affordable Care Act was part of a campaign liberals have been promoting for nearly a century—the campaign to make sure every American has access to medical care without fear of financial ruin. And while the Act won’t, by itself, achieve that goal, it goes a long way to doing so and, no less important, puts in place an institutional framework that will make that achievement possible. At the same time, the Act also develops the tools our society can use, in the coming years, to make health care more efficient—something we desperately need to do in order to keep public and private finances under control.

Can we say anything like that about the tax deal? I don’t think so. The tax deal will help boost the economy in the next year or two. That’s no minor thing, given the economic struggles so many Americans face. But it's also a temporary change. If we’re lucky, the time Obama has bought with this temporary extension will allow him to do in two years what he couldn’t do now—and end the upper income tax cuts once and for all. That’s also no minor thing, given how big those tax cuts are and the impact that will have on our fiscal future. But that outcome is also very speculative—a lot more speculative, I would argue, than the argument that the Affordable Care Act will improve people’s lives.

To be clear, I take seriously the suggestion, from administration officials, that there was no way to win this tax fight even back in the summer. I also think the terms of the deal are as good as this Congress was likely to approve in this political environment. Like Robert Greenstein, of the Center on Budget and Policy Priorities, I’d like to see the measure pass (although I’d hardly object if liberal Democrats used whatever bargaining leverage they have to extract better terms). But I also think the critics of the tax deal have much stronger case than the critics of the Affordable Care Act did.