Cases this year on campaign speech, religion, juvenile crime, federal power and Miranda warnings resulted in an ideological split among the justices, and on every occasion, Sotomayor joined the liberal bloc.
"There was some anxiety among liberals last year that she would be to the right of Justice [David] Souter, especially on criminal law, but so far that has not been borne out," Cornell University law professor Michael Dorf said of Sotomayor and her predecessor. "She is clearly part of the liberal wing."
It's not clear, however, that President Obama's first court appointee can be called a liberal "activist," because her major dissents so far have come when a conservative majority has shifted the law.
Last week, Sotomayor wrote her first strong dissent in a 5-4 decision holding that a suspect who is warned of his rights and fails to "unambiguously" call for a halt can be questioned for hours. Police are "not required to obtain a waiver" of the suspect's rights, the court said.
"Today's decision turns Miranda upside down," Sotomayor wrote. Her 23-page dissent quoted extensively from the 1966 opinion in Miranda vs. Arizona. "A heavy burden rests with the government," it said, "to demonstrate that the defendant had knowingly and intelligently waived his privilege against self-incrimination." As Sotomayor saw it, the conservative majority was quietly overruling that principle without admitting it.
She has not been a reflexive vote for criminal defendants, however. In two other cases this year, she voted against claims from convicts who said their Miranda rights were violated. And in January, she wrote the opinion for a 7-2 majority rejecting an Alabama death row inmate's claim that his inexperienced lawyer failed him by not telling the jury about his mental deficiencies. The lawyer's strategy may have been "debatable," Sotomayor said, but it did not call for overturning the verdict.
In this term's other major crime and punishment case, the liberal bloc prevailed with a key vote from Sotomayor. She joined a 5-4 opinion holding that it is cruel and unusual punishment to impose a life prison term without possible parole on an offender who is younger than 18 and who did not commit murder.
Edward Whelan, a conservative legal analyst, said he was not surprised by her record. "Sotomayor masqueraded as a judicial conservative at her confirmation hearings, but her record indicates she will be a doctrinaire liberal," he said.
But there are few signs of "empathy" — a term President Obama was faulted for using when speaking of prospective judges — in Sotomayor's work so far, though it is still early in her career on the high court.
Last month, Sotomayor spoke for the court in rejecting a claim from a Los Angeles immigrant who died a gruesome death from cancer. He had a growth that had gone untreated for months — despite his repeated pleas for medical attention — while he was locked in a federal detention center.
Shortly before his death, Francisco Castaneda sued the U.S. Public Health Service doctors who ignored his pleas, and he won a preliminary ruling in California. Unswayed, Sotomayor said, "We are required to read the statute according to its text," and the law allows suits only against the U.S. government, not against employees of the Public Health Service.
Friends of Sotomayor say she is feeling swamped by the heavy workload. "She's been blown away by the difficulty and intensity of the job. She's been working seven days a week," said Los Angeles lawyer Nancy Gray, who was in Washington recently to visit her old friend.
June can be a trying time at the court. The justices need to resolve more than two dozen pending cases by the end of the month. They include a test of the 2nd Amendment and its right to bear arms, and a college campus dispute in which the rights of Christian students and gay students are in conflict.
By the end of the month, Sotomayor will be ready to leave Washington for a break, her friend said. "She is looking forward to spending some time back in New York," Gray said.