How does the court release its rulings?
It announces the opinions from the bench beginning at 10 a.m., Washington time. As soon as Chief Justice John Roberts says an opinion is about to be issued, court employees begin handing out copies to reporters. That means the first word of the health-care decision will probably come from news reports. As with arguments, the court doesn't permit video or live audio coverage of its opinion announcements. The court will post a copy of the decision on its website soon after it is issued.

The people in the courtroom may be among the last to know the outcome. The justice who wrote the opinion will give a summary — and may not say immediately what the bottom line is.

Might the news of the decision leak out before it's issued?
Leaks of any sort are rare at the court and leaks about pending decisions are all but nonexistent. The justices demand — and get — secrecy from their law clerks and the few court employees who know about rulings in advance.

What are the possibilities?
There are a variety of ways the court could rule:

(1) It could uphold the entire statute, the Patient Protection and Affordable Care Act.

(2) The court could strike down part of the law. This could take several forms. It might invalidate only the requirement that most Americans get insurance or face penalties, the so-called individual mandate that was once championed by Republicans as an alternative to Democratic proposals for a single government-run health system.

More likely, based on the arguments in late-March, they would also reject related provisions that require insurers to cover people with pre-existing medical conditions and charge them the same rates as other policyholders. The administration as well as those challenging the law agree that rejecting the mandate while keeping the related provisions would create a situation in which only patients with costly health issues would obtain insurance. That would lead to higher premiums, which would prompt healthy policyholders to drop coverage, causing more rate increases.

The court might also invalidate the law's expansion of the Medicaid program for the poor, which is intended to provide coverage to about 16 million uninsured people.

(3) The court could strike down the entire law.

(4) It could decide that the challenge to the insurance requirement by a group of 26 states and a small-business trade organization is premature and must wait until the penalties for failure to obtain insurance are actually imposed after the mandate goes into effect in 2014.

Which justices are the likely swing votes?
Based on the arguments in March, the pivotal votes belong to Roberts and Justice Anthony Kennedy, two of the five Republican appointees on the nine-member court. During the two-hour session during the arguments on the insurance mandate, both aimed the bulk of their questions at the lawyer representing the Obama administration. At the same time, they left their likely votes in doubt by similarly directing questions toward the challengers to the law.

What are the central legal issues?
The fate of the insurance requirement will turn on the court's interpretation of three parts of the Constitution. The first is the commerce clause, which says Congress may “regulate commerce with foreign nations and among the several states.” The court has relied on the commerce clause to uphold laws such as the 1964 Civil Rights Act.

The court previously has extended the reach of the commerce power through the necessary-and-proper clause. That provision says Congress may “make all laws which shall be necessary and proper for carrying into execution” its enumerated powers.

Congress also has power under the Constitution to “lay and collect taxes, duties, imposts and excises.” The Obama administration says the tax clause provides a second, independent constitutional basis for the law.

The Medicaid issue centers on the Constitution's spending clause, which authorizes Congress “to pay the debts and provide for the common defence and general welfare of the United States.” The Supreme Court has said that provision lets Congress put conditions on federal funds. The states say they are being unlawfully coerced.

The court also will say whether a law known as the Anti-Injunction Act makes much of the case premature. That law says that taxes can't be challenged until they're assessed.

What did the lower courts say
They were divided. Of the four federal appeals courts to rule, two upheld the law, one declared the insurance mandate unconstitutional and the fourth said the Anti-Injunction Act made a court review premature.

Has there been a similar case so close to an election?
The closest parallel comes from 1935 and 1936, when a series of high court rulings voided parts of President Franklin Roosevelt's New Deal, economic programs designed to respond to the Great Depression.

When was the last time a Supreme Court ruling was so eagerly anticipated?
It was Dec. 12, 2000, the day the Supreme Court decided Bush v. Gore and sealed the presidential election for George W. Bush. As with health care, reporters crammed the court's press room, rows of cameras stood outside and the country sat by the television awaiting the news.

One difference: The justices didn't take the bench that day to announce their ruling. At about 10 p.m. Washington time, court employees simply handed out the opinion, and history was made.

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