President Barack Obama's health care overhaul, a law that touches core political divisions in the United States and an issue central to the Republican bid to deny him a second term, has been taken before the Supreme Court for three days of hearings
The court began hearing arguments on Monday morning, while demonstrators chanted outside. "Care for you, care for me, care for every family", supporters shouted. A half-dozen opponents yelled, "We love the Constitution!"
Since Obama signed the controversial legislation into law two years ago, 26 states have challenged the constitutionality of the overhaul, the largest expansion in the nation's social safety net in more than four decades.
At the law's core is the requirement that most people buy health insurance by 2014 or pay a tax penalty. Challengers say congress exceeded its constitutional power to regulate commerce with this so-called individual mandate.
The fight against the law, aimed at extending health insurance to more than 30 million Americans, has further inflamed deep divisions in a country knocked off kilter by the Great Recession and embroiled in a political battle about the role of government.
The administration argues congress has ample authority to do what it did. If its action was rare, it is only because congress was dealing with a problem that has stymied Democratic and Republican administrations for decades: How to get adequate health care to as many people as possible, and at a reasonable cost.
And reams of court filings attest that the changes are being counted on by people with chronic diseases, touted by women who have been denied coverage for their pregnancies and backed by Americans over 50 but not yet old enough to qualify for Medicare, the federal health insurance program for Americans when they reach age 65
All four Republicans battling for the nomination to challenge Obama in the November election have vowed to repeal the health care overhaul, provided the conservative-dominated Supreme Court doesn't strike it down in a decision that is expected in June.
Republican presidential candidate, Rick Santorum, speaking outside the high court on Monday said the bill "has far-reaching consequences for the economic health of our country and for basic liberty in our society and that’s why this decision and the debate that is going on is fundamental".
Until the health care law, the US was the only major developed country without a national health care system.
Republicans are leading the fight to kill the law either via the court or through congressional repeal. They say the worst fears about what they derisively call "Obamacare" already have come to pass in the form of higher costs and regulations, claims that the law's supporters dispute.
Polls have consistently shown the public is at best ambivalent about the benefits of the health care law and that a majority of Americans believe the insurance requirement is unconstitutional.
Opponents have at times refereed to the plan as "Obamascare", alleging that "death panels" will decide if critical patients are worth treating and equates the plan with "socialism".
The hearings this week will be closely followed for clues about what the nine Supreme Court justices are thinking and how they will weigh voting along party lines against case law precedent.
The court has four liberal-leaning justices appointed by Democratic presidents - two by Obama - and five conservatives appointed by Republican presidents. In order for the law to stand as written, at least one of the conservative justices will have to join the liberals in ruling to uphold the law.
People hoping for a glimpse of the action waited in line all weekend for the relatively few seats open to the public. The justices allotted the case six hours of argument time, the most since the mid-1960s. The usual time is an hour, with 30 minutes for each side.
The court, which has steadfastly denied access to television cameras, will release audio recordings of the arguments on the same day they take place.
The first arguments Monday concern issues around what is known as the "mandate" that all Americans buy or have health insurance coverage, a law similar to the healthcare reform former Massachusetts governor and Republican presidential candidate hopeful Mitt Romney pioneered in the state in 2006.
That provision in Obama's law was designed to protect the profits for insurance companies by expanding the number of people who are customers.
That is envisioned as an offset to losses as a result of federal laws preventing insurers from denying coverage to people with medical problems, forbidding them from dropping coverage for individuals who become seriously ill and limiting how much they can charge older people.
By refusing to issue a ruling because the mandate provision does not go into effect for two years, the justices would avoid rendering a decision just months before the presidential election.
The justices also will take up whether the rest of the law can remain in place if the insurance mandate falls.
By 2019, about 95 per cent of the country will have health insurance if the law is allowed to take full effect, the Congressional Budget Office estimates.