With a decision by the court expected this month, here is a look at potential outcomes:
Q: What if the Supreme Court upholds the law and finds Congress was within its authority to require most people to have health insurance or pay a penalty?
A: That would settle the legal argument, but not the political battle.
The clear winners if the law is upheld and allowed to take full effect would be uninsured people in the United States, estimated at more than 50 million.
Starting in 2014, most could get coverage through a mix of private insurance and Medicaid, a safety-net program. Republican-led states that have resisted creating health insurance markets under the law would face a scramble to comply, but the U.S. would get closer to other economically advanced countries that guarantee medical care for their citizens.
Q: On the other hand, what if the court strikes down the entire law?
A: Many people would applaud, polls suggest.
Taking down the law would kill a costly new federal entitlement before it has a chance to take root and develop a clamoring constituency, but that still would leave the problems of high costs, waste, and millions uninsured.
Some Republicans in Congress already are talking about passing anew the more popular pieces of the health law.
But the major GOP alternatives to Obama’s law would not cover nearly as many uninsured, and it’s unclear how much of a dent they would make in costs. Some liberals say Medicare-for-all, or government-run health insurance, will emerge as the only viable answer if Obama’s public-private approach fails.
Q: What happens if the court strikes down the individual insurance requirement, but leaves the rest of the Affordable Care Act in place?
A: Individuals would have no obligation to carry insurance, but insurers would remain bound by the law to accept applicants regardless of medical condition and limit what they charge their oldest and sickest customers.
Studies suggest premiums in the individual health insurance market would jump by 10 percent to 30 percent.
Experts debate whether or not that would trigger the collapse of the market for individuals and small businesses, or just make coverage even harder to afford than it is now. In any event, there would be risks to the health care system. Fewer people would sign up for coverage.
The insurance mandate was primarily a means to an end, a way to create a big pool of customers and allow premiums to remain affordable. Other forms of arm-twisting could be found, including limited enrollment periods and penalties for late sign-up, but such fixes would likely require congressional cooperation.
Unless there’s a political deal to fix it, the complicated legislation would get harder to carry out. Congressional Republicans say they will keep pushing for repeal.
Q:What if the court strikes down the mandate and also invalidates the parts of the law that require insurance companies to cover people regardless of medical problems and that limit what they can charge older people?
A: Many fewer people would get covered, but the health insurance industry would avoid a dire financial hit.
Insurers could continue screening out people with a history of medical problems; diabetes patients or cancer survivors, for example.
That would prevent a sudden jump in premiums. But it would leave consumers with no assurance that they can get health insurance when they need it, which is a major problem that the law was intended to fix.