WASHINGTON — Starting Monday, the U.S. Supreme Court will hear six-hours of arguments on President Obama’s health care reform legislation.

The arguments will be the longest in decades, and for good reason: The court is tasked with determining the constitutionality of the Affordable Care Act, the highlight legislative accomplishment of Obama’s first term and one that will dramatically affect the lives of the 50 million Americans without health insurance, the companies that employ them and the pool of individuals already covered by health insurance — in other words, pretty much everybody.

At the heart of the case, the justices will need to decide if the law’s mandate that everyone purchase health insurance is permissible under the U.S. Constitution’s commerce clause, which gives Congress the power to regulate commerce that occurs both across state lines and within one state if it affects the broader national economy. There are other issues in the case, but the individual mandate is the most pressing one the court will consider, University of Minnesota constitutional law professor Timothy Johnson said.

“It really is going to be a discussion of whether or not Congress has the power under the commerce clause to mandate that every individual in the United States needs to buy health insurance,” he said.  “In the end, this case comes down to the individual mandate.”

The court has been taking commerce clause cases since the 1820s, and except for a brief period of conservative jurisprudence in the 1930s, it has generally given a lot of leeway to the federal government to regulate commerce. The court will use several cases as precedent, Johnson said, but two will play a bigger role than others:

•  Wickard v. Filburn: In 1942, the Supreme Court ruled that the federal government has the right to regulate economic activities as simple as the crops a farmer grows for his own private use, since such an action would change what he purchases on the open market, and therefore have an effect on the economy at large;

•  Gonzales v. Raich: In 2005, the court ruled that a federal law superseded a California statue legalizing medical marijuana. Individuals growing and distributing their own marijuana were influencing the national marijuana market, and thus, Congress has the right to step in regulate the practice.

Both cases affirmed Congress’s right to regulate activities even on that smallest scale since they can inevitably influence the economy as a whole.

“The majority made very clear that anything that’s really economic in nature, illegal or legal, is regulable by Congress,” Johnson said. “The court has had a pretty extensive reading of the commerce clause, even in the conservative era.”

A different type of case

But opponents have argued that the Affordable Care Act case is different than any the court has heard before: rather than passing a law banning individuals from activities that affect the economy, Congress is instead requiring them to do something — in this case, buying health insurance.

That’s the argument the 11^th Circuit Court of Appeals made when it struck down the individual mandate in a 2-1 decision last August.

“This economic mandate represents a wholly novel and potentially unbounded assertion of congressional authority: the ability to compel Americans to purchase an expensive health insurance product they have elected not to buy, and to make them re-purchase that insurance product every month for their entire lives,” the majority wrote.

Other courts, however, have backed the mandate, and Reuters notes that conservative jurists have, in two occasions, written the opinions that upheld it, finding that Congress has an interest in regulating an individual’s insurance coverage because everyone, with or without insurance, will enter and influence the health care market at some point.

“The argument is that the decision not to purchase health care insurance is effectively an economic decision,” Chicago-Kent College of Law professor Sheldon Nahmod said in a video previewing next week’s cases for the Oyez Supreme Court website. “The decision not to buy health care insurance in a situation when everyone, at some point, with our without health care insurance, is going to need health care means that people without health care insurance are costing money that the rest of us are paying for. The argument is that that’s just not fair.”

How will they rule?

So in a nutshell: precedent suggests the court will side with Congress, upholding its ability to require insurance coverage because without it, the uninsured have an indelible impact on the broader health care industry. But conservatives have argued that Congress cannot compel a citizen to purchase anything, and at least one court sided with their argument.

The only people who matter now are the nine members of the Supreme Court, and we can use their voting record to at least hint as to where they’ll come down in this case.

Most observers predict the court’s four liberals to uphold the law, and at least two conservatives — Clarence Thomas and Samuel Alito — to overturn it. Anthony Kennedy is expected to be a swing vote (he upheld Congress’s regulatory authority in the marijuana case above), and Reuters suggests that John Roberts and even the conservative Antonin Scalia could be, too.

That last name’s a bit surprising — Scalia is a bastion of conservatism on the court, but he did side with the federal government in the Gonzales case. Oyez highlights Scalia’s concurring opinion: “Where economic activity substantially affects interstate commerce, legislation regulating that activity will be sustained.”

A final decision from the court is expected to come down over the summer.

Devin Henry can be reached at dhenry@minnpost.com. Follow him on Twitter: @dhenry