It was also the term in which Chief Justice Roberts emerged as the member of the court at its ideological center, his vote the crucial one in closely divided cases, a role no chief justice has played since 1937. He was in the majority in all but one of the term’s 5-to-4 or 5-to-3 decisions.
But the chief justice was not alone in guiding the court toward the center: The percentage of 5-to-4 rulings dropped to a little more than 20, down from an average of 30 in the previous two terms.
Several major decisions were decided by 7-to-2 votes, including ones on subpoenas for President Trump’s financial records and the rights of religious employers. In some ways, the most prominent losers this term were the members of the court on its far right (Justices Clarence Thomas and Samuel A. Alito Jr.) and far left (Justices Ruth Bader Ginsburg and Sonia Sotomayor). They were the least likely to be in the majority in divided cases.
Chief Justice Roberts, 65, is a work in progress.
“This is the term where those of us who thought we understood John Roberts came to understand that we didn’t,” said Irv Gornstein, the executive director of Georgetown’s Supreme Court Institute. “I know some are already spinning out theories to explain how his votes fit into a coherent judicial philosophy. But as it was happening, it was one shock after another.”
The trend is clear, said Lee Epstein, a law professor and political scientist at Washington University in St. Louis. “He is drifting left at a statistically significant rate — and at a rate roughly resembling Souter’s liberal turn in the 1990s,” she said.
Justice David H. Souter, who was appointed in 1990 by President George Bush, soon emerged over his two decades on the court as a leading member of its liberal wing, much to the distress of his conservative sponsors.
The chief justice was in the majority in divided cases 94 percent of the time, trailed by Mr. Trump’s two appointees: Justice Brett M. Kavanaugh, who voted with the majority 89 percent of the time, and Justice Neil M. Gorsuch, who voted with it 83 percent of the time. Together, Professor Epstein said, those three justices make up the “soft middle” of the court.
In divided cases, the chief justice voted with Justice Kavanaugh 89 percent of the time, and Justice Gorsuch 77 percent.
Other rates of agreement were more striking. Chief Justice Roberts voted with Justice Elena Kagan, a member of the court’s liberal wing, 69 percent of the time. By contrast, he voted with Justice Alito 63 percent of the time — the same rate as with Justice Stephen G. Breyer, another liberal. And the chief justice voted with Justice Thomas just 54 percent of the time.
Over all, Chief Justice Roberts’s rate of agreement with Democratic appointees was 61 percent, up from 44 percent in the previous term.
Mr. Trump has had a bad run at the court over his time in office, becoming the first president since Franklin D. Roosevelt whose administration lost more cases than it won.
The result was that a court dominated by five Republican appointees, including two named by Mr. Trump, disappointed conservatives at a notable rate. “This term spectacularly frustrated the conservative ambition to transform the Supreme Court into the G.O.P.’s lap dog,” said Justin Driver, a law professor at Yale.
The court did its work in the middle of a pandemic, hearing arguments by telephone and allowing live audio coverage, both firsts. It typically ends its term in late June, but this year it issued its last decisions in July, which has not happened since 1996.
The court postponed arguments in 10 cases to the term that starts in October, and it decided just 53 argued cases with signed opinions, the smallest number since the 1860s. During the Spanish flu epidemic in the term that started in 1918, the court also postponed arguments but nonetheless decided 163 cases, or more than three times as many as the current court.
It was hardly a uniformly liberal term. Eight of the 12 closely divided cases featured the classic lineup, with the five Republican appointees in the majority. In two, on abortion and immigration, Chief Justice Roberts voted with the four Democratic appointees. In one, on Native American rights, Justice Gorsuch voted with them. (In the last 5-to-4 decision, in a copyright case, the alliances were scrambled.)
Justice Gorsuch drew fire from the right for his majority opinion in Bostock v. Clayton County, Ga., ruling that a landmark federal civil rights law protects L.G.B.T.Q. workers. The court’s four-member liberal wing and the chief justice joined his opinion in the 6-to-3 decision.
The retirement in 2018 of Justice Anthony M. Kennedy, who wrote the majority opinions in all four of the earlier landmark gay rights decisions, had made that outcome uncertain.
“With Justice Kennedy’s departure, some court watchers justifiably feared that the movement toward accepting gay equality would stall, or perhaps even be reversed,” Professor Driver said. “Instead, in a historic decision, the court redoubled its egalitarian efforts and even afforded protection to the trans community. Until quite recently, such a decision would have been unfathomable.”
Justice Gorsuch’s opinion employed textualism, the mode of statutory interpretation that looks to the words of the law under consideration rather than the intentions of the lawmakers who voted for it.
Professor Gornstein said the reaction from the right was telling.
“Rather than celebrating the opinion as the high-water mark for textualism,” he said, “the conservative reaction has been to excoriate Justice Gorsuch as a betrayer of the conservative cause, leading to this question: Do conservatives want a justice who will follow the judicial method favored by conservatives, or do they want a justice who uses all the tools available to reach conservative policy results?”
Sarah Harrington, a Supreme Court specialist with Goldstein & Russell, said Chief Justice Roberts has exerted a moderating influence on colleagues inclined to lurch right.
“I think we can expect that he will oversee a general shift toward more conservative rulings over time,” she said, “but he continues to pump the brake on that shift, adhering for now to recent precedent and requiring the federal government to follow administrative-law rules in order to implement its conservative policy agenda.”
An example of adherence to recent precedent was the chief justice’s vote in the 5-to-4 decision to strike down a Louisiana law on the ground that the court had invalidated the identical law from Texas just four years before.
An example of requiring the government to follow administrative law principles was Chief Justice Roberts’s majority opinion in a 5-to-4 decision rejecting the Trump administration’s justifications for trying to shut down a program protecting the Dreamers.
The court was exceptionally active in cases involving religious institutions, siding with them three times in a row. The court ruled that state programs supporting private schools must include religious ones, that the Trump administration could allow employers with religious objections to deny contraception coverage to female workers and that employment discrimination laws do not apply to many teachers at religious schools.
Not all of the court’s actions are reflected in data on argued cases. The justices have also ruled on a series of emergency applications, some prompted by the pandemic. Chief Justice Roberts joined the court’s four liberals, for instance, in a 5-to-4 order rejecting a California church’s challenge to the state’s shutdown policies.
But he twice joined his conservative colleagues in similar orders making it harder to vote in Wisconsin and Texas. “When it comes to state efforts to suppress the vote,” Professor Gornstein said, “the chief continues to vote in lock step with the rest of the right.”
Over all, though, Professor Epstein said, the court has provided a welcome contrast to the partisan turmoil around the nation.
“This term, most justices — and Roberts, in particular — modeled centrist, nonpartisan behavior for the country,” she said. “The data show a decline in 5-4 decisions, more agreement across party lines and a roughly 50-50 split in liberal and conservative decisions. The big cases, too, went ‘one for you, one for me,’ which may help bolster the court’s legitimacy.”
Alicia Parlapiano contributed reporting.