Call it the main event: after a day puzzling over whether Obamacare’s fines on those who don’t buy insurance constitute a tax or a penalty—an important threshold issue, to be sure, but one that hasn’t quite captured the public’s imagination—the Court today will hear oral argument regarding one of the most important issues before it in 65 years: whether the Constitution empowers Congress to require that virtually all Americans purchase or obtain health insurance coverage.

The answer to that question will determine whether the federal Leviathan truly remains a government of limited, enumerated powers, or whether the division of powers between the federal government, on the one hand, and the states and the people, on the other, has finally been obliterated.  In short, today’s argument cuts to the very heart of our “federalist” republic, pitting against each other two drastically different visions of the role of the national government in our lives.

But you knew that.  The real question, of course, is how the justices see the matter.  Here are a few things to watch for at oral argument today:

First, if the mandate is unprecedented . . . well, what then? ObamaCare’s supporters have made muchperhaps too much—of the simple point that, just because Congress’s exercise of a power is “unprecedented,” doesn’t mean that it’s unconstitutional. But as the Court has recognized, if “earlier Congresses avoided use of [a] highly attractive power, we would have reason to believe that the power was thought not to exist.” No one seriously disputes that the mandate is novel, but how will the justices respond when Paul Clement, arguing for the state challengers, cites that as evidence of its unlawfulness? That could be more than just interesting.

Second, how deeply will the Court wade into the economics of health care? One of the government’s arguments is that health care is somehow “unique” because everyone will use it at some point and that the unique economics of the market for health care or health insurance somehow justify a mandate to purchase a product from a private party—but just this one time, promise!  Along these lines, the government has offered numerous explanations of why it is that the mandate is absolutely necessary to fix the health care market. —Dusting off its college economics book, the government argues that mandates are essential to addressing uncompensated care, or adverse selection, or premium spirals, or the negative impacts of other government regulations.  The more the Court gets into the policy weeds, the better the government’s chances of success, due to the Court’s traditional deference to the political branches over matters of policy.  In constitutional terms, this should be a simple case; making it complicated is to the government’s advantage.

On the other hand, there are some rather nifty facts and inconvenient truths in the brief for the entity that brought the case against the federal government, the National Federation of Independent Business (NFIB).  There is, for example, the NFIB’s lawyers will be able to demonstrate that the primary purpose of the mandate is to force healthy, young Americans to pay inflated insurance rates to the insurance industry to cover bad policy regulations, rather than just prevent the uninsured to become free riders on the system.  Mike Carvin, who represents those challenging Obamacare, will mention these facts—or respond to questions about them— that counter the government’s faux-economic story when he takes his turn at the podium 85 minutes into the two-hour session.  Carvin won’t want to spend too much time on these facts for the reasons explained above.  He can’t win on them alone; he’s got to focus primary attention to the moral and constitutional high ground of his position.  But as any baseball fan knows, you have to play good defense and stop the other side’s scoring opportunities in order to switch back to offence.

Third, what about RaichRaich was the Court’s 2005 decision that found that Congress could criminalize the possession of small amounts of marijuana within a state as part of its goal to prevent interstate commerce of marijuana. Today the government will likely claim that Raich gives Congress the authority to regulate almost anything as long as its end goal is to regulate an interstate market.  When examining Raich, it’s important to remember Justice Scalia’s concurring opinion, which offers a narrower view that defines more precisely the relationship between the Commerce Clause and the Necessary and Proper Clause.  The justices’ questioning today should shed light on what they think Raich meant and how it applies in this instance.  In particular, watch for questions on whether the mandate is “proper.”  Analogies to the rule against Congress “commandeering” the states or state officials will spell doom for the government’s position.  Chief Justice Roberts, Kennedy, and Scalia are key.

Fourth is a simple one: keying off a Heritage Foundation paper that laid the groundwork for this litigation, the challengers of Obamacare will likely draw a distinction between activity and inactivity, arguing that the Commerce Clause gives Congress no license to regulate the latter.  Are the justices receptive to or dismissive of that that idea?  It doesn’t matter what Justices Ginsburg, Breyer, Sotomayor, or Kagan say on this issue, since their vote for the government is assumed.  But even a partial receptivity or concern about regulating inactivity by the Chief and Justice Kennedy would be significant.

Fifth, what else will the Chief say to tip his hand?  Known as a committed constitutionalist, the Chief Justice has an appreciation for the structural features of the Constitution.  However,he also has a reputation (albeit exaggerated) for avoiding controversial decisions and attempting to foster consensus on the Court where it may not easily lie. One such decision was in a case implicating federalism, but there was a lot more going on. Often, when the Chief has a compromise position in mind, he’ll float it at oral argument, sometimes through questions to counsel that push back at the more aggressive implications of their arguments.  His questions to Clement and Carvin, who will both argue for the challengers, will be important.

Finally, the government will walk a fine line between arguing that the mandate is necessary and proper to its broader regulatory scheme but avoiding the implication that, if the mandate falls, the entire ObamaCare statute will have to fall with it.  Justice Alito, who has a talent for drilling down on the most difficult and unpleasant questions to counsel, may try to wrong-foot the Solicitor General on this point.  And all the justices may join in haranguing the Solicitor General on what his “limiting principle” is, or how his theory of the Commerce and Necessary and Proper Clauses doesn’t swallow up all other government powers, national and state.  If the Solicitor General can’t give a convincing answer on what the limits of Congress’s power will be if ObamaCare is ok, this ball game may be over with a win for the challengers.

But don’t forget that this is a World Series of sorts.  The double-header scheduled on Wednesday features arguments on ObamaCare’s costly and coercive Medicaid expansion and the all-important argument on “severability,” i.e., whether any portion of the law can survive if either of its main pillars is knocked down.  And by my count, a win for the challengers in games five, six or seven will effectively decide the constitutional match.

Todd Gaziano is the Director of the Center for Legal & Judicial Studies at The Heritage Foundation.