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The U.S. Supreme Court building June 27, 2012 in Washington, D.C. As the Supreme Court prepares to decide the constitutionality of the Affordable Care Act, states are waiting to see if their gambles about whether the law would be overturned will pay off. - 

Jeff Horwich: Among the constitutional issues the Supreme Court decides today are the mandate that all Americans buy health insurance and a big expansion of Medicaid. Thirty million uninsured Americans have a stake in the ruling.

And so do the 50 states, as Marketplace's Dan Gorenstein reports.

Dan Gorenstein: About a quarter of states have moved aggressively to comply with the new law, that includes using federal dollars to set up health exchanges -- think Travelocity but to buy insurance.

Peter Lee heads up California’s exchange. And while he really doesn’t think this will happen, Lee says if the court strikes the whole law, it means millions of Californian’s will remain uninsured.

Peter Lee: It would be the equivalent of a major earthquake or a tsunami hitting the state of California.

But what if the court goes in the other direction and upholds the law, or most of it? Then another dozen states or so -- the resisters -- all of a sudden face tough deadlines to create exchanges and expand their Medicaid programs.

Of course, under that scenario, insurers will be knocking on the door whether a state has fully complied with the law, or dragged its feet, says Case Western Reserve health finance professor J.B. Silvers.

J.B. Silvers: They’re basically going full speed ahead, this is a winning market for the insurance companies.

Later this morning, we’ll find out just how much the rules for that market will change.

I’m Dan Gorenstein for Marketplace.

Follow Dan Gorenstein at @dmgorenstein