New York Times

WASHINGTON — Chief Justice John G. Roberts Jr. usually displays his supple intellect and competitive nature at Supreme Court arguments, where he makes points and punctures the positions of the lawyers who appear before him.

But on Wednesday, hearing one of the most important cases in his almost 10 years on the court, he turned into a sphinx. He asked just a few questionsas other justices repeatedly talked over one another during arguments over the fate of President Obama’s health care law.

Before the arguments started, the Obama administration was confident it could count on the court’s four liberal members to allow tax subsidies that help millions of people buy health insurance in the roughly three dozen states where the federal government runs insurance exchanges.

But would Chief Justice Roberts provide the crucial fifth vote to support the divisive health care overhaul, as he did in 2012? Or would he join his usual conservative allies, who seemed eager to strike down the law?

That remains a mystery, given the chief justice’s reticence. He did ask one question that provided the slightest of hints that he was looking for a way to allow the subsidies, but perhaps only temporarily. That would be consistent with the incremental approach he has taken in campaign finance and voting rights cases.

In general, though, lawyers on both sides emerged from the argument uncertain about how to answer a question they had been mulling for months: Is the chief justice prepared to be cast once again by fellow conservatives as an ally of the Obama administration — and traitor to their cause?

The reaction to his 2012 vote among conservatives on and off the court was brutal. Justices Antonin Scalia, Anthony M. Kennedy, Clarence Thomas and Samuel A. Alito Jr. issued a rare joint dissent. The conservative news media, notably The Wall Street Journal’s editorial page, accused the chief justice of betraying the Constitution.

Since then, he has expressed concern about the public’s views of the court, saying that partisan politics never figure in its deliberations. He bristles at accusations that the court is a political body.

In remarks in September at the University of Nebraska, he said he was worried that the partisan rancor and gridlock in Washington would affect perceptions of the court. “I don’t want it to spill over and affect us,” he said. “That’s not the way we do business. We’re not Republicans or Democrats.”

Had Chief Justice Roberts voted the other way in 2012, the court would have been subject to such criticism, fairly or not. The bottom line would have been that the court’s five Republican appointees struck down a Democratic president’s signature legislative achievement in an election year over the dissents of the four Democratic appointees.

But the experience of abandoning his usual allies seemed to have left him bruised. After the decision was issued, he promptly left for Malta to teach a course on the history of the Supreme Court.

How unusual was Chief Justice Roberts’s vote in the 2012 health care case? Very. It remains the only 5-to-4 decision in which he joined the four liberal members of the court, Justices Ruth Bader Ginsburg, Stephen G. Breyer, Sonia Sotomayor and Elena Kagan.

The closest analogy came the last time he failed to ask a question in a major case, in arguments last year over the constitutionality of abortion protest buffer zones in Massachusetts. The decision in the case, McCullen v. Coakley, was nominally unanimous in striking down the buffer zones.

But the court was sharply divided on the rationale for the decision. Chief Justice Roberts, joined by the four liberals, issued a narrow majority opinion that left the state with other ways to address problems around abortion clinics. The four other conservative justices issued a pair of concurring opinions calling for a more sweeping ruling.

The chief justice’s silence that time suggested a strategic mind at work, one calculating a way to draw liberal votes toward a unanimous decision.

But unanimity seems out of the question in the new health care case, King v. Burwell, No. 14-114.

At Wednesday’s argument, the administration was heartened by some of the questions posed by Justice Kennedy, and it seemed possible that he would provide the fifth vote they need.

That could leave Chief Justice Roberts with difficult choices in the pair of decisions likely to conclude the term. He gets to choose the justice who will write the majority opinion — but only if he is in the majority. Otherwise, the longest-serving justice in the majority makes the assignment.

Given that chief justices like to influence the court’s opinions, it is perhaps not a coincidence that Chief Justice Roberts was in the majority 92 percent of the time last term, trailing only Justice Kennedy.

The court will hear the term’s other blockbuster case, on same-sex marriage, on April 28. If the voting in that case tracks that in the last major gay rights case, Justice Kennedy will join the court’s four liberals to strike down bans on such unions.

As the senior justice in that group, Justice Kennedy would be likely to assign the decision to himself. He is the author of all three of the Supreme Court’s landmark gay rights decisions, and it would be a surprise if he handed off the biggest one to another justice.

If the same coalition votes to uphold nationwide insurance subsidies, the term could end with two liberal decisions assigned and perhaps written by Justice Kennedy, leaving the leader and namesake of the Roberts court on the sidelines. That cannot be an appealing prospect, and it could prompt the chief justice to look for a narrow, provisional ground to uphold the subsidies.

Near the end of Wednesday’s arguments, he asked Solicitor General Donald B. Verrilli Jr. to clarify one point.

As a backup argument, Mr. Verrilli had said the justices should defer to the interpretation of the Internal Revenue Service, which says subsidies are available nationwide, if they found the health care law itself to be ambiguous.

“If you’re right,” Chief Justice Roberts asked Mr. Verrilli, “that would indicate that a subsequent administration could change that interpretation.”

Mr. Verrilli, resisting a victory that might vanish in 2016, urged the court to rule on the basis of the statute itself.

That comment from Chief Justice Roberts was the closest he came to probing the core of the case before him. It did almost nothing to tip his hand.

The best evidence of his views may well still be found in part of his 2012 health care opinion, one joined by no other justice.

“It is not our job,” he wrote, “to protect the people from the consequences of their political choices.”