The U.S. Supreme Court is poised to rule this week on PresidentBarack Obama's health-care overhaul, a law that would extendinsurance to at least 30 million Americans and reshape an industrythat makes up about 18 percent of the country's economy.

The decision, coming little more than four months before theNovember election, will mark the first time the court has ruled ona president's signature legislative accomplishment in the middle ofhis re-election bid.

Here's what to expect and look for in the ruling:

Will the court rule today?
It might,though a decision later in the week is at least as likely. Thecourt has five decisions left to issue, including on an Arizona lawcracking down on illegal immigration, and the justices will presentthem over two or perhaps three days. Based on past practice, themost likely second opinion day is Thursday, June 28. We'll knowmore after the court makes its rulings today.

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

The people in the courtroom may be among the last to know theoutcome. 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'sissued?
Leaks of any sort are rare at the court andleaks about pending decisions are all but nonexistent. The justicesdemand — and get — secrecy from their law clerks and the few courtemployees who know about rulings in advance.

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

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

(2) The court could strike down part of the law. This could takeseveral forms. It might invalidate only the requirement that mostAmericans get insurance or face penalties, the so-called individualmandate that was once championed by Republicans as an alternativeto Democratic proposals for a single government-run healthsystem.

More likely, based on the arguments in late-March, they wouldalso reject related provisions that require insurers to coverpeople with pre-existing medical conditions and charge them thesame rates as other policyholders. The administration as well asthose challenging the law agree that rejecting the mandate whilekeeping the related provisions would create a situation in whichonly patients with costly health issues would obtain insurance.That would lead to higher premiums, which would prompt healthypolicyholders to drop coverage, causing more rate increases.

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

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

(4) It could decide that the challenge to the insurancerequirement by a group of 26 states and a small-business tradeorganization is premature and must wait until the penalties forfailure to obtain insurance are actually imposed after the mandategoes into effect in 2014.

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

What are the central legalissues?
The fate of the insurance requirement willturn on the court's interpretation of three parts of theConstitution. The first is the commerce clause, which says Congressmay “regulate commerce with foreign nations and among the severalstates.” The court has relied on the commerce clause to uphold lawssuch as the 1964 Civil Rights Act.

The court previously has extended the reach of the commercepower through the necessary-and-proper clause. That provision saysCongress may “make all laws which shall be necessary and proper forcarrying into execution” its enumerated powers.

Congress also has power under the Constitution to “lay andcollect taxes, duties, imposts and excises.” The Obamaadministration says the tax clause provides a second, independentconstitutional basis for the law.

The Medicaid issue centers on the Constitution's spendingclause, which authorizes Congress “to pay the debts and provide forthe common defence and general welfare of the United States.” TheSupreme Court has said that provision lets Congress put conditionson federal funds. The states say they are being unlawfullycoerced.

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

What did the lower courts say
They weredivided. Of the four federal appeals courts to rule, two upheld thelaw, one declared the insurance mandate unconstitutional and thefourth said the Anti-Injunction Act made a court reviewpremature.

Has there been a similar case so close to anelection?
The closest parallel comes from 1935 and1936, when a series of high court rulings voided parts of PresidentFranklin Roosevelt's New Deal, economic programs designed torespond to the Great Depression.

When was the last time a Supreme Court ruling was soeagerly anticipated?
It was Dec. 12, 2000, the daythe Supreme Court decided Bush v. Gore and sealed the presidentialelection for George W. Bush. As with health care, reporters crammedthe court's press room, rows of cameras stood outside and thecountry sat by the television awaiting the news.

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

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