How could a law as popular as the landmark health-care reform known as Obama-care be under such harsh attack on its fifth anniversary? The answer may lie in the fact that the nation's body politic is headed in a far less promising direction than the health of its citizens - whose access to the means to live healthier lives expanded immeasurably with President Obama's signature on the Affordable Care Act five years ago today.

As for the popularity of Obamacare, despite negative (but improving) public perceptions of the law, the more than 16 million Americans who have gained health coverage so far can hardly be wrong. No health initiative since Medicare has done more to reduce the number of people without insurance, at risk of serious illness going untreated or straining the charity-care capacity of vital urban teaching hospitals.

Yet the law is under legal challenge before the Supreme Court for the third time in its short existence, this time based on the spurious claim that Congress never intended to subsidize insurance premiums for the majority of Obamacare policyholders. By seizing on a few words in a 900-plus-page document, opponents argued before the high court this month that the subsidies could be paid only through state-run health-insurance exchanges rather than the federal government's HealthCare.gov.

Not only do many legal experts find that notion absurd, but it would mean that Democratic members of Congress - given that not a single Republican voted for the law - inserted a poison pill to doom their own legislation. That simply doesn't make any sense.

Without the premium subsidies, and with so many millions of Obamacare policies issued through the federal insurance marketplace, the law would collapse. (Most Republican governors, including Tom Corbett, refused to set up state exchanges as part of the continuing effort to undermine the ACA.)

On such flimsy legal grounds, and with such devastating potential consequences, even the court's conservative bloc has to understand the high stakes of the case, which is to be decided by June. Along with the health outlook of millions, the very credibility of the high court could be called into question.

Were the court to scuttle the law, it would deprive individuals of a broad range of health benefits - chief among them the assurance that no one can be denied access to adequate, affordable coverage. Beyond that, a sudden U-turn on Obamacare would threaten a multibillion-dollar boost to the health-care sector through an infusion of new paying customers, as well as innovations that promise to turn or at least temper the growth of health-care costs.

Indeed, rather than worrying that this will be the last time to blow out the candles, this five-year mark should be a moment to celebrate the sweeping progress the country has made under the Affordable Care Act.