Q. What if the court strikes down the mandate and 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 would be able to continue screening out people with a history of medical problems, such as diabetes patients or cancer survivors.
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, a major problem the law was intended to fix. Other economically developed countries guarantee health insurance for their citizens.
A related requirement limits premiums charged to older adults. Currently people in their late 50s and early 60s can face premiums as much as six or seven times higher than those charged to 20-year-olds. The law says insurers may charge older adults no more than three times what they charge younger ones.
Administration lawyers say the insurance requirement goes hand in hand with the coverage guarantee and cap on premiums, and have asked the court to get rid of both if it finds the mandate to be unconstitutional.
Q. What happens if the court throws out only the expansion of the Medicaid program?
A. Throwing out the expansion would severely limit the law's impact because roughly half of the more than 30 million people expected to gain health insurance under the law would get it through the expansion of Medicaid, the federal-state health insurance program for low-income people.
The law would effectively bring under Medicaid everyone making up to 138 percent of the federal poverty level. That works out to about $15,400 for an individual, $30,650 for a family of four. Most of those who would be added to the Medicaid rolls are low-income adults without children.
But a potentially sizable number of those low-income people might still be eligible for government-subsidized — though probably more expensive — private insurance under other provisions of the law. Private coverage will probably be more expensive for taxpayers 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, reaching directly into the wallets of state taxpayers.
The administration counters that the federal government is paying all of the initial cost of the expansion and 90 percent in perpetuity, well above what Washington contributes for regular Medicaid. Moreover, when Congress created Medicaid in 1965 it also served notice on the states that program rules could change in the future. This is only the latest of many such changes.
The Supreme Court took on this issue even though none of the district or appeals courts that heard health care lawsuits had any problem with the Medicaid expansion.
"We don't have any lower court that has struck down this (Medicaid) provision, so there is no precedent from the lower courts on how to handle it," said Diane Rowland, a Medicaid expert with the nonpartisan Kaiser Family Foundation. "They all upheld it."
Q. What happens if the court decides that the constitutional challenge is premature?
A. The wild card, and least conclusive outcome in the case, probably also is the least likely, based on what justices said during the arguments. No justice seemed inclined to take this path, which involves the court's consideration of a technical issue. The federal appeals court in Richmond, Va., held that the challenge to the insurance requirement has to wait until people start paying the penalty for not purchasing insurance. The appeals court said it was bound by the federal Anti-Injunction Act, which is intended to facilitate tax collections and keep the government operating. That law says federal courts may not hear challenges to taxes, or anything that looks like a tax, until after they are paid.