The U.S. Supreme Court is a busy place this time of year. So when the justices announced that, starting March 26, they would hear six hours of arguments on the health care reform law—the most time it has dedicated to any one case in decades—the gravitas of the issue became clear to all.

The Patient Protection and Affordable Care Act (PPACA) is perhaps the most profound change to health care since Medicaid was instituted in 1965. "This case deserves the hype it's getting," says Gregory Magarian, a law professor at Washington University in Saint Louis School of Law.

The case is not just a political lightning rod—and whatever decisions emerge from the Court in the early summer will likely do little to diffuse the partisan tensions around the issue. What's really at stake in the case is individuals' access to health care.

Signed into law March 23, 2010, PPACA is expected to expand access to health care to an additional 32 million uninsured people in the U.S.—unless all or part of it is struck down by the Supreme Court.

"If this law's thrown out, I think we're resigned to the status quo, which is a lot of people without access to health care for a long time," says Larry Levitt, an expert at the Kaiser Family Foundation, a nonprofit, nonpartisan policy analysis organization. "I don't think there's any question about what lack of access to health care means: people get treated later, and some people die earlier as a result."

That also means continued health care cost increases, an expenditure that already eats up some $2.6 trillion a year—about a fifth of all U.S. spending.

At issue are two major provisions: the requirement that everyone have health insurance—the so-called individual mandate—and an expansion of Medicaid benefits, which would help more people afford insurance in the first place. "If the Court rejects either or both of those, it would have far-reaching implications for how health care reform would work—or even if the law would work at all," Levitt says. With fewer people insured, premiums would become even more expensive.

One of the unusual things about the legal challenge is that most of the law's big changes have not yet gone into effect, which has muddied the debate about how it will likely affect people's lives in practice. The individual mandate, for example, is not slated to begin until 2014. As more provisions are rolled out, Magarian notes, the law's benefits for individuals will likely become clearer to many. "For a lot of people this law is going to be a desirable thing on a personal level." he says.

From a public health perspective, the only argument against the law is that it should be even more aggressive in ensuring that people have access to affordable health care, says John McDonough, a professor at Harvard University's School of Public Health.

The Court will be hearing arguments about four segments of the law over the course of three days. What is at stake for each of these issues?

Individual health

Much of the outcry about the PPACA has centered on a need to preserve individual rights—that is, no law should require that people get health coverage. But the case before the court, Magarian explains, "isn't about that at all." The question in front of the Court pertains to state rights. "I think that would surprise a lot of people." This confusion, he posits, might be behind some of the recent polls that show about two thirds of Americans favor repealing the whole law part and parcel. As Levitt points out, if the Court overturns the PPACA, the states are well within their constitutional bounds to require their residents to purchase health insurance (as they already do with auto insurance).

Essentially is the Court must grapple the question of congressional power—and whether it can regulate interstate business to this extent. Regardless of the outcome, "there's no way of resolving it to everybody's satisfaction," Magarian says. "I think the government has the better argument, but this really is at some level, a question of first principles."

But one of the big questions is whether other provisions of the law will be viable, financially, without requiring everyone to get health insurance. The law also requires insurance companies to insure anyone regardless of their health needs and at a reasonable premium. Such provisions depend in large part on insurance companies being able to spread the high medical costs of the few among the premiums of the many, thereby making health care more affordable for all. Otherwise, people will tend to wait until they need insurance (that is, when they are very sick or had an accident) before they buy it. "It's kind of like letting people buy homeowner's insurance when their house is on fire—it just doesn't work very well," Levitt says.

If the Affordable Care Act is implemented without the individual mandate, some 12.5 million people would remain uninsured, according to the RAND Corp., a nonprofit, nonpartisan research group.

Because many of those people will nonetheless need care they cannot afford, insurance companies would ultimately have to absorb the cost, which they in turn would pass on to policyholders as increased premiums. Government expenditures on each new insurance recipient would also double (raising total spending by $10 billion in 2016).

The Court will hear arguments about the individual mandate on Tuesday.

Medicaid for more

The law's expansion of Medicaid, to be heard on Wednesday, compels states to broaden the number of people eligible for the program, which would mean millions more people who cannot afford health insurance would be able to enroll. If states refuse to expand their programs, whose costs would be split between the states and the federal government, they risk losing federal money for other programs.

Twenty-six states have challenged this provision, saying it is an unfair financial burden for them. But Magarian thinks this part of the case does not hold much water legally. States already have had plenty of other federal programs imposed on them by Congress, so this new one would not be all that unusual. If other aspects of the law were not already being challenged, "I wouldn't think the Supreme Court would bother with it," Magarian says. If the court upheld the individual mandate but threw out the Medicaid provision, it would hoist an especially large burden on people in the lower income brackets who are currently excluded from Medicaid assistance but would be required to get coverage.

Beyond Medicaid and the mandate

The law, of course, is not just about individual insurance and Medicaid. Its 906 pages hold a plethora of other provisions, some of which have already taken effect. In the second day of hearings, the Court will hear arguments about whether these other issues—such as allowing individuals under the age of 26 to be on their parents' health insurance plans and tax breaks for small businesses that provide insurance to employees—can be kept if other parts of the law get thrown out. According to the Court's charge, it "should rule as narrowly as it can," Magarian explains. And that means only excising what it deems unconstitutional.

Because some of these smaller provisions are in force, Levitt points out, the Court will probably not overturn them.

Taxing law

One way the court could get out of a ruling now is if it decides that the requirement that people obtain health coverage (or else face a fine) amounts to a tax. If the justices decide that it does, they could invoke the 19th-century Anti-Injunction Act, which limits the power of federal courts to interfere with lawsuits in state courts and, if applied in this case, would not allow a tax to be repealed until after people have already been required to pay it. In this case, that would mean postponing a ruling until 2015.

"It would be an awfully beautiful dodge," Magarian admits. But, he says, despite its appeal, "they're not going to do that if it's not the right answer legally."

This topic will kick off the hearings on Monday.

What might happen

Most experts agree that the Supreme Court is unlikely to dispatch with the law in its entirety. Magarian suggests that the recent poll numbers showing a majority of Americans favoring a complete elimination likely betrays confusion about what the end result of the law will be: affordable health care for millions more Americans.

"The big stuff hasn't actually happened yet," Magarian says of the Affordable Care Act's major provisions. "Many more people will have occasion to be happy about it than unhappy about it."

Still, it is a government program, he notes, which some people just categorically oppose. But "it's a government program that gives people something that they don't have." And as it stands, it is market-driven, allowing for competition within the insurance market rather than a single-payer system. To stay that way, McDonough says, the individual mandate needs to be retained: "The health insurance system is more healthy and functions better as a market with an individual mandate."

If the Supreme Court does strike down parts of the law, Congress will likely have to make adjustments to try to balance out some of the economics. But, Levitt says, "both sides would have an incentive to come to the table at that point," noting that big political standoffs have gotten a little stale with the public as of late.

And if the law were to be reversed now, it would mean hospitals and insurance companies would have to backpedal, which could be disruptive to business and planning.

But if all or large parts of it end up falling, health reform will likely be slow to come up for serious consideration again. The most recent major discussion about health care reform was in the 1990s. If the PPACA stands, it would be the first major step in improving the availability of health services since the Social Security Act of 1933 and the 1965 amendments to the act that created Medicare and Medicaid. "This is not the kind of law that happens every administration," McDonough says.

Regardless of the Supreme Court decision, however, McDonough says far more important for public health is the election in November. If those who support the law control enough federal power, they could revive it even if the Court strikes it down; and if those opposed to the law wind up with the majority, they could dispatch it even if the Court upholds it. So from a public health standpoint, McDonough notes, the presidential and congressional elections are "much more consequential to the law that whatever the Supreme Court does."

To follow the Supreme Court hearings, audio will be posted to their site daily.