WASHINGTON ¨C U.S. Chief Justice John Roberts, who cast the decisive vote in 2012 to beat back the first major challenge to President Barack Obama¡¯s health care law, kept his cards close on Wednesday.

And the man who occupies the center chair on the Supreme Court¡¯s mahogany bench and often dominates arguments seemed to remain deliberately inscrutable.

Roberts asked few questions, none revealing his view of the challenge to the crucial tax-credit subsidies that help low- and moderate-income people buy insurance under the 2010 law. His first question came late in the arguments of the challengers¡¯ lawyer and was, in fact, more of a joke.

As liberal justices pounded Michael Carvin for altering his stance on the necessity of the tax-credit subsidies to Obamacare from his view in the failed 2012 court challenge, Roberts remarked: ¡°Mr. Carvin, we¡¯ve heard talk about that other case. Did you win that other case?¡±

As spectators began to laugh, Roberts said, ¡°So maybe it makes sense that you have a different story today.¡±

Carvin, at the time representing a small-business group, lost when Roberts joined the court¡¯s four liberals to uphold Obamacare.

On Wednesday, Carvin argued on behalf of Virginians enlisted as plaintiffs by a libertarian group opposed to Obama¡¯s signature domestic policy achievement.

In 2012, Roberts, a shrewd 60-year-old former corporate lawyer appointed by Republican President George W. Bush, drew the condemnation of fellow conservative justices and much of the right-wing legal community for preserving Obamacare.

Roberts never responded publicly to conservatives¡¯ claims he was a traitor or to liberals¡¯ praise of him as a savior. His few words on Wednesday suggested he knows he is being watched as the possible pivotal vote again.

One clue to Roberts¡¯ thinking might have emerged near the end of the 85-minute oral argument when U.S. Solicitor General Donald Verrilli said the court regularly defers to Internal Revenue Service interpretation of tax laws.

Here, the IRS has said the tax-credit subsidies should be given to people who buy insurance on federally run as well as state exchanges.

¡°If you¡¯re right,¡± Roberts said, ¡°that would indicate that a subsequent administration could change that interpretation.¡±

Verrilli said the next administration would ¡°need a very strong case¡± to make a switch.

Roberts may be suggesting he is open to ruling for the government while ensuring Obama¡¯s successor in the White House an opportunity to reinterpret the law.

His fellow justices will get the first glimpse of Roberts¡¯ views on Friday when they privately take their customary preliminary vote on the week¡¯s cases. The vote always starts with him.