But the debate over health care reform -- which will intensify again next week as the Supreme Court hears oral arguments on challenges to the law's mandate on individuals to buy insurance -- involves more than competing philosophies or political strategies. At its core, it raises an irreducibly tangible question: what, if anything, to do about the nearly 50 million Americans who today lack health insurance?

Those millions of uninsured rarely intrude into the promises from GOP congressional leaders and the party's presidential field to defend liberty by repealing Obama's plan. But ignoring them doesn't make them go away. If the 2012 election rewards Republicans with enough leverage in Washington to erase Obama's initiative, they will face the choice of finding an alternative means to expand coverage or allowing the number of those without insurance to grow, with far-reaching consequences not only for the uninsured but for those with insurance as well.

Without some policy intervention, there's little question that access to health insurance will continue to decline. Since 2000, the number of the uninsured has jumped from 36.6 million to 49.9 million, about one-sixth of all Americans.

That number would have been even higher if an additional 20 million people over that period had not obtained coverage through Medicaid and the Children's Health Insurance Program. This growth partially offset the unrelenting erosion in employer-based care: The share of Americans obtaining coverage from their employer has declined every year since 2000, in good times and bad.

Earlier this month, the Congressional Budget Office forecast that, absent the new health-care law, the number of uninsured would rise to 60 million by 2020. That large a pool of uncovered Americans would create enormous strain for the health-care system.

The uninsured themselves would feel the most immediate effect, of course -- studies show they are much more likely than those with coverage to defer or entirely forego needed care. But such an increase would also produce upward pressure on premiums for the insured as providers, especially hospitals, raise prices for those with coverage to offset the cost of uncompensated care to those without it. "The idea that repeal [of health-care reform] is somehow going to lower your premium is folly," says Len Nichols, director of George Mason University's Center for Health Policy Research and Ethics. More likely, he argues, repeal would increase premiums.

Obama's health-care law, whatever its other virtues or flaws, represents a serious effort to break this cycle. CBO, echoing earlier projections, estimated last week that it would cover 33 million of the uninsured. No Republican has offered a plan to cover anywhere near so many. In 2009, the Congressional Budget Office estimated that the principal House Republican alternative to Obama's proposal would cover only 3 million of the uninsured.