â€œThe fate of health care reform is where it was yesterdayâ€"in the hands of Supreme Court Justice Anthony Kennedy.â€ So writes Slateâ€™s David Weigel, reflecting the accepted wisdom about U.S. District Judge Roger Vinsonâ€™s decision striking down the Patient Protection and Affordable Care Act. And Weigel may be right. Justice Anthony Kennedy often does cast the crucial fifth vote, sometimes siding with the Courtâ€™s liberal bloc, other times with the conservatives. And the legal challenge to ObamaCare certainly wonâ€™t be over until the Supreme Court weighs in. But the Kennedy-as-decider scenario also assumes that all four conservatives will vote against the individual mandate. Can we be so sure about that?

Until two weeks ago the speculation centered mostly on Justice Antonin Scalia, who famously concurred with the liberal majority in Gonzales v. Raich (2005), the case where Congressâ€™ authority to regulate interstate commerce was held to include medical marijuana cultivated and consumed entirely within a single state. So Scaliaâ€™s commitment to a less expansive reading of the Commerce Clause was far from guaranteed. But then last month Scalia joined an opinion written by Justice Clarence Thomas which dissented from the Courtâ€™s refusal to hear an important Commerce Clause case. According to Thomas and Scalia, the Court had permitted a lower court ruling to stand whose â€œlogic threatens the proper limits on Congressâ€™ commerce power and may allow Congress to exercise police powers that our Constitution reserves to the States.â€ Keep in mind that it takes four votes for the Court to hear a case and that Scalia could have kept his vote secret like the other seven justices. Instead, he sided with Thomas and sent a very clear signal that heâ€™s still willing to enforce a few limits on Congressâ€™ power â€œto regulate commerce…among the several states.â€

That leaves Justice Samuel Alito and Chief Justice John Roberts. Roberts is the real question. As Charles Fried, a former solicitor general under President Ronald Reagan and a respected elder in the conservative legal movement, told Politico, â€œI think thereâ€™s a good chance it will be a 6-3 decision in favor of constitutionality.â€ Hereâ€™s how Fried explained it to Politicoâ€™s David Nather:

Chief Justice John Roberts â€œdoes not believe the Commerce Clause allows you to do everything and anything,â€ but heâ€™s not â€œan adventurerâ€ and therefore might not go so far as to strike down the mandate.

Itâ€™s an important point. Roberts has repeatedly described himself as a fan of â€œjudicial modestyâ€ and stressed his belief in the importance of respecting precedent. Thatâ€™s a stance that might lead him to uphold the individual mandate as consistent with the Courtâ€™s already broad reading of the Commerce Clause. But then again, Roberts has left himself some wiggle room, writing in Citizens United, for example, that itâ€™s acceptable to strike down precedent â€œwhen the precedentâ€™s underlying reasoning has become so discredited that the Court cannot keep the precedent alive without jury-rigging new and different justifications to shore up the original mistake.â€

So it's still a guessing game. But itâ€™s also a serious mistake to assume that Kennedy is the only ObamaCare vote we need to watch.