From left, U.S. Supreme Court Chief Justice John Roberts and Justices Anthony Kennedy, Ruth Bader Ginsburg, Stephen Breyer, Sonia Sotomayor and Elena Kagan applaud before President Obama's State of the Union speech in February 2013. (Reuters)

You can never be far from the center of any discussion of the “Roberts court” when your name is John G. Roberts Jr.

But as the Supreme Court last week ended a decade of oral arguments under the chief justice’s leadership, Roberts came in for special attention as not only the public face of the court but also its most scrutinized player.

There’s good reason for that.

In one of the court’s two blockbuster cases, about the implementation and continued viability of President Obama’s Affordable Care Act, Roberts is likely to play the pivotal role.

In the other, about same-sex marriage, Roberts was the only one of the nine justices last week who appeared to be searching for a middle ground that might allow the court to hold off on deciding whether the Constitution requires states to allow gay couples to marry.

And in cases that the court has decided this term, less than half of the docket, Roberts already has surprised.

In a case involving former UPS employee Peggy Young, he sided with liberals to make it easier for pregnant workers to sue if employers do not provide health-related accommodations to their work routines.

And last week he faced the wrath of fellow conservatives for breaking a streak of decisions invalidating campaign-finance regulations as unconstitutional restrictions on free speech. Roberts wrote for a five-member majority that said Florida and other states were free to forbid judicial candidates from directly soliciting campaign contributions.

As long as the court is ideologically divided, Justice Anthony M. Kennedy will most often remain the court’s tie-breaker in major cases.

But the 60-year-old Roberts is the court’s future. If he zigs when everyone thinks he’s going to zag, reporters, law professors and legal commentators go on the alert. Headline writers at the New Republic got ahead of the author’s analysis when they wondered last week, “Is John Roberts Drifting Left?” But you get the idea.

Roberts’s decision in the judicial campaign contributions case is the most surprising of the term. At oral argument earlier this year in Williams-Yulee v. The Florida Bar — challenging the state’s rules that say a judicial candidate must use a committee to raise campaign funds rather than directly asking for contributions — Roberts sounded as if his mind were made up.

“You have a situation where the people in the state have said we’re going to have judges elected and we’re going to recognize that you can contribute to judges because of there are contribution limits,” Roberts told the lawyer representing the bar.

“It seems to me you’re under a great burden trying to figure out how you’re going to fix that without contravening the First Amendment.”

Roberts figured it out himself. Florida’s rule “advances the state’s compelling interest in preserving public confidence in the integrity of the judiciary,” he wrote. “This is therefore one of the rare cases in which a speech restriction withstands” a free-speech challenge.

Kennedy and Justice Antonin Scalia wrote bristling dissents about how Roberts “flattened” First Amendment precedents, in Scalia’s words. Roberts replied that the two should take a deep breath.

Roberts mocked Scalia’s assertion that Florida’s rule suggested a hostility to electing judges and had “nothing to do with the appearances created by judges’ asking for money.”

“Nothing?” Roberts replied.

Likewise, he accused Kennedy of overheated rhetoric, noting his dissent’s use of the phrase “state censorship” and its charge that the rule “silenced” public debate.

“A reader of Justice Kennedy’s dissent could be forgiven for concluding that the court has just upheld a latter-day version of the Alien and Sedition Acts,” Roberts wrote.

The opinion instead reinforced two of Roberts’s chief themes. One is that judges are different. It is something he has preached to a public increasingly angry about partisanship in all levels of government.

And second, Roberts made clear that almost all other forms of campaign regulation, save perhaps disclosure, are suspect.

“Politicians are expected to be appropriately responsive to the preferences of their supporters,” Roberts wrote. “Indeed, such ‘responsiveness is key to the very concept of self-governance through elected officials.’ ”

Roberts was quoting himself, from last term’s ruling in McCutcheon v. Federal Election Commission striking down aggregate limits on campaign contributions.

Both for the campaign-finance decision and the chief justice’s potential role in the court’s coming decisions on Obamacare and same-sex marriage, Roberts became the main topic of conversation when the liberal Constitutional Accountability Center held a panel discussion about the term last week.

“I think arguably this term is going to be the defining term for the Roberts court,” said Elizabeth B. Wydra, the group’s chief counsel.

She held out hope that Roberts, who dissented in the U.S. v. Windsor decision striking down part of the federal Defense of Marriage Act, would find a way to rule for same-sex marriage in the current case. “I don’t think it’s impossible,” she said cautiously.

Paul M. Smith, a lawyer who has been involved in the major gay rights cases before the court, thought that unlikely. “He’d basically have to eat his dissent in the DOMA case,” Smith said.

Smith said that the test for Roberts will be the fight over the Affordable Care Act, where challengers say the words of the statute do not allow subsidies for those who buy health insurance on a federal exchange, only those set up by states.

If Roberts votes for a technical reading of the law instead of agreeing with the administration about the intent of Congress in passing the legislation, Smith said, “that will change how he is perceived for quite a while.”

(Conservatives complain that liberals think the only way the court can be perceived as nonpartisan is for the Republican-appointed justices to agree with the administration. Why wouldn’t it be just as nonpartisan for the Democratic-appointed justices to decide the administration is wrong, they say.)

The conservative on last week’s panel, Yaakov Roth, a Washington lawyer who clerked for Scalia, said he didn’t think Roberts’s legacy would be determined by either case.

A defeat for the Obama administration in the health-care case would be a victory for Scalia’s advocacy of a textualist reading of the law, Roth said.

Same-sex marriage and gay rights are linked to Kennedy, he said, and Roberts need not worry about his legacy if he finds there is no constitutional right to marriage.

“I don’t know how this case is going to be seen in 30 or 50 years,” Roth said. “But he’s certainly not the only person on the court who is skeptical of this claim. I think 10 years ago, everyone on the court might have been skeptical of this claim.”