“If it’s measured in terms of readiness to overturn legislation, this is one of the most activist courts in history,” Justice Ginsburg said in August in an interview with The New York Times. “This court has overturned more legislation, I think, than any other.”

Chief Justice Roberts said he had a better option: he was about to leave for Malta, where he would teach a two-week class on the history of the Supreme Court. “Malta, as you know, is an impregnable island fortress,” he said on Friday, according to news reports. “It seemed like a good idea.”

 

The decision was a victory for President Obama and Congressional Democrats, affirming the central legislative pillar of Mr. Obama’s presidency. The ruling upheld the individual mandate requiring nearly all Americans to obtain health insurance or pay a penalty.

The questions from the justices indicated that at least some of them were considering either striking down just the requirement, often called the individual mandate, or the entire law.

“Can you create commerce in order to regulate it?” Justice Anthony M. Kennedy asked the lawyer, Solicitor General Donald B. Verrilli Jr., only minutes into the argument.

The decision in the case, expected by June, will have practical consequences for tens of millions of Americans without health insurance, and it may affect Mr. Obama’s re-election chances.

Those questions have been the toughest ones for the Obama administration’s lawyers to answer in court appearances around the country over the past six months. And they are likely to emerge again if, as expected, the Supreme Court, as early as Monday, agrees to be the final arbiter of the challenge to President Obama’s signature health care initiative.

That was a sort of rebuke to President Obama, who had said that empathy was precisely the quality that separated legal technicians like Chief Justice John G. Roberts Jr. from great justices.

Justice Sotomayor would have none of it.