A federal judge in Florida had so ruled in February 2011: "Because the individual mandate is unconstitutional and not severable, the entire Act must be declared void." But a federal appeals court subsequently overruled on the severability question, while upholding the individual mandate's unconstitutionality. Opponents of the law say the individual mandate is crucial to its overall impact, since it is the main funding mechanism for the expansion of a range of other programs. This might be the one question on which the justices will ultimately agree in favor of the government.

Four: Medicaid "coercion" (the national policy implications issue) 1 p.m. ET Wednesday, one hour of oral arguments

This hearing will look at whether states can be forced by the federal government to expand their share of Medicaid costs and administration, with the risk of losing that funding if they refuse.

The 28 GOP-led states bringing separate lawsuits say the new law's significant expansion of the social safety net unconstitutionally "coerces" state governments. That program is administered by the states with a combination of federal and state money, currently requiring coverage only for poor children and their parents or caretakers, adults with disabilities and poor individuals 65 or older. The "coercion" issue was surprisingly added to the health care debate by the justices.

The overall impact

Both sides of the issue agree what the high court decides on these four questions could have monumental implications for the regulatory ability of the federal government to set long-term national policy goals in areas such as the environment, education and the workplace.

Some states have long complained their autonomy is being eroded by creeping federal intervention on spending matters. Article 1 of the Constitution gives Congress the power "lay and collect ... taxes to pay the debts and provide for the common defense and general welfare of the United States" and to "regulate commerce ... among the several states."

Such authority has long been broadly interpreted, including when imposing conditions on recipients, be they individuals or states. No federal court has ever ruled states have been unlawfully coerced when they accept conditions or strings attached to federal funds. The Supreme Court in 1987 affirmed that congressional discretion.

Starting in 2014, PPACA's Medicaid changes would make millions of additional Americans eligible for benefits by raising the income level they earn and still qualify. That would include all adults up to 133% of the federal poverty line. The tricky question is that states are not forced to agree to the law's incremental Medicaid increases, spread out over six years. But the states say abandoning their participation as a result would be a financial, social and political catastrophe -- one which they cannot realistically foresee. Their needy citizens rely on Medicaid, states argue, but the law's expansion of the program could cripple state budgets, currently on average about 20%. That could threaten other state spending priorities.

So the long-standing fight over "federalism" and the leverage the national government wields over states might soon reach epic levels with a high court decision either strengthening or limiting congressional authority on this and potentially a host of other regulatory areas.