In arguments before the Supreme Court this week, the Obama administration might have done just enough to keep the Affordable Care Act from being ruled unconstitutional. Those who believe in limited government had better hope so, at least.

If Obamacare is struck down, the short-term implications are uncertain. Conservatives may be buoyed by an election-year victory; progressives may be energized by a ruling that looks more political than substantive. The long-term consequences, however, are obvious: Sooner or later, a much more far-reaching overhaul will be inevitable.

The three days of oral argument did not unfold the way many experts had expected. Confident predictions that the administration would prevail by a lopsided margin became inoperative as soon as the justices began pummeling Solicitor General Donald Verrilli with pointed questions.

In the end, however, Verrilli gave the skeptical justices what they were looking for: a limiting principle that allows them, should they choose, to defer to Congress and uphold the law.

At the heart of the legislation is the requirement that individuals purchase health insurance or pay a fine. It became clear by their questioning that the court's five conservatives -- including Justice Anthony Kennedy, who sometimes votes with the liberals -- see this mandate as a significant expansion of the federal government's reach and authority.

Verrilli argued that the mandate is permissible under the clause of the Constitution giving the government the power to regulate interstate commerce. Justices demanded to know where this authority ends. Kennedy seemed to be genuinely looking for a limiting principle.

And Verrilli gave him one. The market for health insurance is inseparable from the market for health care, he argued, and every citizen is a consumer of health care. Those who choose not to buy health insurance require health care anyway -- often expensive care at hospital emergency rooms -- and these costs are borne by the rest of us in the form of higher premiums.

I think Verrilli made his case. The court is supposed to begin with the assumption that laws passed by Congress are constitutional. Justices don't have to like the Affordable Care Act in order to decide it should remain in effect.

But it's going to be a close call. What if they strike down the law?

The immediate impact will be the human toll. More than 30 million uninsured Americans who would have obtained coverage will be bereft. Other provisions, such as forbidding insurance companies to deny coverage based on pre-existing conditions presumably would also be invalidated.

Eventually, however, our health care system will be restructured. It has to be. The current fee-for-service paradigm, with doctors and hospitals being paid through for-profit insurance companies, is needlessly inefficient and ruinously expensive.

When people talk about out-of-control government spending, they're really talking about rising medical costs that far outpace any conceivable rate of economic growth. The conservative solution -- shift those costs to the consumer -- is no solution at all.

Our only choice is to try to hold the costs down. If this law doesn't pass constitutional muster, the obvious alternative is to emulate other industrialized nations that deliver equal or better health care outcomes for half the cost. A single-payer system will go from being politically impossible to being, in the long run, fiscally inevitable.