In the most important case of his 17-year tenure, Chief Justice John Roberts found himself entirely alone.

He had worked for seven months to persuade his colleagues to join him in merely chipping away at Roe v. Wade, the 1973 decision that established a constitutional right to abortion. But he was outflanked by the five justices to his right, who instead reduced Roe to rubble.

In the process, they humiliated the nominal leader of the court and rejected major elements of his jurisprudence.

The moment was a turning point for the chief justice. Just two years ago, after the retirement of Justice Anthony Kennedy made him the new swing justice, he commanded a kind of influence that sent experts hunting for historical comparisons. Not since 1937 had the chief justice also been the court’s fulcrum, able to cast the decisive vote in closely divided cases.

Roberts mostly used that power to nudge the court to the right in measured steps, understanding himself to be the custodian of the court’s prestige and authority. He avoided what he called jolts to the legal system, and he tried to decide cases narrowly.

But that was before a crucial switch. When Justice Amy Coney Barrett, a conservative appointed by former President Donald Trump, succeeded Justice Ruth Bader Ginsburg, the liberal icon, after her death in 2020, Roberts’ power fizzled.

“This is no longer John Roberts’ court,” Mary Ziegler, a law professor and historian at the University of California, Davis, said Friday.

The chief justice is now in many ways a marginal figure. The five other conservatives are impatient and ambitious, and they do not need his vote to achieve their goals. Voting with the court’s three liberals cannot be a particularly appealing alternative for the chief justice, not least because it generally means losing.

Roberts’ concurring opinion in Friday’s decision, Dobbs v. Jackson Women’s Health Organization, illustrated his present and perhaps future unhappy lot. He had tried for seven months to persuade a single colleague to join his incremental approach in the case, starting with carefully planned questioning when the case was argued in December. He failed utterly.