Today's outcome is likely to be a factor in the presidential campaign and help define John Roberts' legacy as chief justice. But the court's ruling almost certainly will not be the last word on America's tangled efforts to address health care woes.
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 have to scramble to comply, but the U.S. would get closer to other economically advanced countries that guarantee medical care for their citizens.
Republicans would keep trying to block the law. They will try to elect likely presidential candidate Mitt Romney, backed by a GOP House and Senate, and repeal the law, although their chances of repeal would seem to be diminished by the court's endorsement.
Obama would feel the glow of vindication for his hard-fought health overhaul, but it might not last long even if he's re-elected.
The nation still faces huge problems with health care costs, requiring major changes to Medicare that neither party has explained squarely to voters. Some backers of Obama's law acknowledge it was only a first installment: Get most people covered, then deal with the harder problem of costs.
Q: What happens if the court throws out only the expansion of the Medicaid program?
A: That would limit the law's impact severely because roughly half of the more than 30 million people expected to gain insurance under the law would get it through the expansion of Medicaid, the federal-state health insurance program for low-income people.
But a potentially sizable number of those low-income people still might be eligible for government-subsidized private insurance under other provisions. Private coverage is more expensive to subsidize than Medicaid.
States suing to overturn the federal law argue that the Medicaid expansion comes with so many strings attached it amounts to an unconstitutional power grab by Washington. The administration says the federal government will pay virtually all the cost and says the expansion is no different from ones that states have accepted in the past.
Read the ruling online: http://www.supremecourt.gov/opinions/11pdf/11-393c3a2.pdf