Opening arguments began today as the U.S. Supreme Court prepares to rule on President Obama's landmark national health care law later this year.
Whatever the nine justices decide, it will be historic.
The so-called individual mandate is the linchpin of the law and came under scrutiny as the nation's highest court launched into its hearing Tuesday.
That provision of the law requires Americans to buy health insurance, and it could unravel President Obama's biggest domestic policy achievement.
The justices must decide how much power the federal government has in forcing every American to purchase a product or enroll in a government program.
Lawmakers have never before used this power, as insurance, while obviously valuable in countless situations, is a product one could theoretically avoid.
Proponents of the Patient Protection and Affordable Care Act, a.k.a. ObamaCare, say it's unprecedented because it's never been this necessary.
Opponents contend it's because the authority doesn't exist, and argue it must be struck down by the high court on grounds of unconstitutionality.
The Supreme Court justices will be looking at three significant constitutional areas to determine whether the Affordable Care Act (ACA) is lawful: