On Tuesday, Roberts was pointed in saying the Texas Court of Criminal Appeals has "misapplied" a 2017 ruling that instructed that court to reconsider its analysis of whether death row inmate Bobby James Moore was intellectually disabled, and thus ineligible for execution.
Less than two weeks ago, Roberts joined the liberals in stopping a Louisiana abortion law that was nearly identical to a Texas law the court had struck down in 2016.
It was a busy day Tuesday, as Justice Ruth Bader Ginsburg rejoined her colleagues for a public hearing for the first time since she underwent lung surgery in December:
• Justice Clarence Thomas called for reconsidering the Supreme Court's landmark decision that made it more difficult for public officials to claim defamation; the court was turning down a request from an accuser of Bill Cosby when Thomas did so.
• The court agreed to hear a case next term that could define the scope of the Clean Water Act, which regulates pollution discharges into what are called "navigable waters." In this case, the Lahaina Wastewater Reclamation Facility in Hawaii first releases water into groundwater, some of which eventually reaches the Pacific Ocean.
Roberts' role in the abortion and death penalty cases were notable partly because he had been in dissent in the original decisions. His actions are not a sign that he has changed his mind; the ruling that the Louisiana law could not go into effect at this time was not a decision on the merits.
But they do seem to be an indication the chief justice believes lower courts must comply with Supreme Court precedents so long as they stand.
"On remand, the court repeated the same errors that this court previously condemned," Roberts wrote, concurring in the majority's finding Tuesday that Moore, the inmate, "is a person with intellectual disability."
The Texas court's review of Moore's case "did not pass muster under this court's analysis last time," Roberts wrote in a separate opinion. "It still doesn't."
The court in an unsigned opinion said the Texas court was wrong to reaffirm that Moore was mentally capable, and eligible for execution. Three of the court's conservatives - Justices Clarence Thomas, Samuel Alito and Neil Gorsuch - noted their disagreement in a dissent written by Alito. He said that the court's instructions in the 2015 ruling on Moore were so gauzy it is no surprise that the Texas court had trouble following them. The proper response, he said, would have been to return the case with more specific instructions, not to take the decision away.
"The court's foray into fact-finding is an unsound departure from our usual practice," Alito wrote.
In a 5-to-3 decision written in 2017 by Ginsburg, the court sent back the case of Bobby James Moore, who fatally shot store clerk James McCardle in a botched robbery in 1980. Moore's decades-long trip through the appeals courts has been marked by conflicting opinions on whether he is intellectually disabled.
Texas's Court of Criminal Appeals eventually determined that he was not. But the Supreme Court concluded that this decision improperly relied on outdated medical standards, borderline IQ scores and a list of unique-to-Texas factors that Ginsburg termed an "invention . . . untied to any acknowledged source."
The Texas court once again considered Moore's intellectual abilities, and again found him competent.
But on Tuesday, the Supreme Court majority was unimpressed: "We have found in its opinion too many instances in which, with small variations, it repeats the analysis we previously found wanting, and these same parts are critical to its ultimate conclusion."
In the Louisiana abortion case, Roberts did not spell out his reasoning. Instead, he joined the liberal justices in keeping the law - which required doctors performing abortions to have admitting privileges at nearby hospitals - from taking effect. Challengers had said it would likely leave only one clinic open, and one doctor who could provide abortions.
It is likely that because of the granted stay, the court will next term consider the merits of the law.
In that stay decision on Feb. 7, Thomas, Alito and Gorsuch also dissented, along with new Justice Brett Kavanaugh.
Thomas' call for overturning the landmark 1964 decision New York Times v. Sullivan came as the court declined to take the case of Kathrine McKee, who accused actor and comedian Bill Cosby of raping her more than 40 years ago. She sued after Cosby's attorney leaked a letter that she said distorted her background to "damage her reputation for truthfulness and honesty," and to shame her.
But the U.S. Court of Appeals for the 1st Circuit said McKee had "thrust" herself into the national (hash)MeToo movement with her allegations. As a public figure, the court said, she had to show that comments about her were made with "actual malice" and disregard for the truth, the standard set by the Supreme Court.
Thomas said he agreed with his colleagues not to accept McKee's "factbound" appeal.
But he launched a detailed critique of the landmark defamation ruling, which he said was a "policy-driven" decision "masquerading as constitutional law." No other justice joined his concurrence.
President Donald Trump has expressed support for making it easier to sue for defamation, and during the campaign - and after - he complained about "hit pieces" in The Washington Post and New York Times.
"I'm going to open up our libel laws so when they write purposely negative and horrible and false articles, we can sue them and win lots of money," Trump said during the campaign. Over the weekend, he complained about a "Saturday Night Live" skit and wondered about "retribution."
Thomas has said the court may have intruded into a space in which it was not needed.
"We should not continue to reflexively apply this policy driven approach to the Constitution," Thomas wrote. "Instead, we should carefully examine the original meaning of the First and Fourteenth Amendments. If the Constitution does not require public figures to satisfy an actual-malice standard in state-law defamation suits, then neither should we."