By David G. Savage

Reporting from Washington—

A Republican-led challenge to the Democrats‘ most ambitious social legislation in a generation goes before the Supreme Court on Monday, with President Obama‘s healthcare law hanging in the balance.

The court’s ruling, expected by the end of June, may decide whether the Constitution puts any limit on Congress’ power to regulate not just healthcare, but the entire economy.

The arguments begin with a technical discussion of whether the proposed penalty for not buying health insurance amounts to a tax. If the justices find that it is, under an old law they may have to postpone ruling on most of the issues until after the penalty goes into effect in 2014.

On Tuesday, the justices will get to the heart of the matter, debating whether Congress has the authority to make people purchase a product: health insurance.

On Wednesday, they will talk about whether the rest of the law can stand on its own even if the insurance mandate is struck down, and the separate issue of whether the federal government’s plan to fund a massive expansion of state Medicaid programs violates states’ rights under the Constitution. 

Since 1936, the justices have not struck down a major federal regulatory law on the grounds that Congress went too far. The court’s forbearance on matters touching Congress’ authority to regulate commerce has allowed Washington’s power to grow, to protect civil rights and the environment, to ensure safer automobiles and drugs, and to help boost the wages and benefits of workers.

All the while, however, conservatives and business groups have insisted there must be a limit. Otherwise, they say, an all-powerful federal government would be free to write its own rules.

Such a limit — if the Constitution indeed sets one — is at the heart of the healthcare case.

Legal scholars on the right and the left see the case as momentous.

“It goes to who we are as a people and what kind of government we have,” said Ilya Shapiro of the libertarian Cato Institute.

The court “is at a crossroads,” said Doug Kendall, president of the progressive Constitutional Accountability Center. If the court “strikes down the law, we’re back to the New Deal era with a progressive president at war with a conservative court.”

To Obama and the Democrats in Congress, the need for the Patient Protection and Affordable Care Act was obvious. Nearly 50 million Americans lack health insurance. When they go to hospitals, the costs are borne by others, including the taxpayers. And all face a loss of insurance if they lose jobs or have serious illnesses or other preexisting conditions.

The only way to prevent those problems was to bring everyone into the system, Obama argued, guaranteeing coverage for all, prohibiting insurance companies from excluding people they didn’t want to cover and requiring, in exchange, that everyone get insurance. Those who could not pay the full cost would be offered subsidies.

Critics, however, say the “government mandate” to buy insurance goes too far. It crosses a line, they say, from reasonable regulation of commerce to a dictate from Washington to engage in commerce.

“This reaches into the living room of a guy who is healthy and doesn’t want to buy health insurance,” said Paul D. Clement, the former George W. Bush administration solicitor general, who represents Republican officials from 26 states. He will try to persuade a conservative-leaning high court that it should break with decades of precedent and void the entire law.

The Supreme Court, signaling the extraordinary nature of the case, agreed to hear six hours of arguments over three days, rather than the usual single hour. The court agreed to also consider Clement’s claim that Congress exceeded the Constitution when it pressed the states to expand the Medicaid program.

Progressives, not surprisingly, see the court’s intervention as ominous. They say the Constitution created a national government to “promote the general welfare.” It did not authorize the court to veto laws that regulate business and commerce in the public interest, they say.

The issue also poses a dilemma for the court’s conservative majority: Just what type of conservatives are they? Do they seek to reimpose conservative principles on the two elected branches of government, or do they hew to the idea of a limited, restrained role for the courts?

Since at least the Ronald Reagan era, conservatives have argued that elected lawmakers, not unelected judges, should decide the major issues of government. Chief Justice John G. Roberts Jr. echoed this theme when he told senators during his confirmation hearings that he saw a modest role for judges, more like an “umpire calling balls and strikes” than a star player.

As conservative Judge Laurence H. Silberman of the D.C. Circuit Court of Appeals wrote in upholding the healthcare law in November, the Constitution left Congress “free to forge national solutions to national problems.”