The Supreme Court on Wednesday signaled it is on the verge of a major curtailment of abortion rights in the United States, and appeared likely to uphold a Mississippi law that violates one of the essential holdings of Roe v. Wade established nearly 50 years ago.

Whether the court would eventually overrule Roe and its finding that women have a fundamental right to end their pregnancies was unclear.

But none of the six conservatives who make up the court’s majority expressed support for maintaining its rule that states may not prohibit abortion before the point of fetal viability, which is generally estimated to be between 22 and 24 weeks of pregnancy.

Chief Justice John G. Roberts Jr., often the most moderate of the conservatives, said Mississippi’s law prohibiting most abortions after 15 weeks was not a “dramatic departure” from viability, and gave women enough time to make the choice to end their pregnancies.

He added: “Why would 15 weeks be an inappropriate line?”

But the other conservatives did not express much interest in rewriting Roe, decided in 1973, or 1992’s affirming decision in Planned Parenthood v. Casey. Rather, they indicated they were open to simply getting rid of both.

The court’s liberal justices said the institution’s reputation would be irreparably damaged if nearly a half-century of its abortion jurisprudence were dismantled because of a change in membership.

During Supreme Court oral arguments on Dec. 1, Justice Sonia Sotomayor pointedly refuted several arguments supporting a Mississippi anti-abortion law. (The Washington Post)

But the nearly two-hour argument seemed to indicate that the three nominees of President Donald Trump — Neil M. Gorsuch, Brett M. Kavanaugh and Amy Coney Barrett — will be key to the outcome.

Oral arguments can be misleading at times, with justices playing devil’s advocate in their questioning. But Wednesday’s questioning and debate will surely raise the hopes of a conservative movement that has made paramount its goal of installing a Supreme Court that would overturn Roe.

There was very little to make abortion rights supporters feel they had a chance at stopping the Mississippi law, and reason for pessimism that Roe and Casey would remain entrenched law.

If the court’s usual practices hold, the justices will take an initial vote on the case Friday. But it is probably months before a decision will be announced; compromise is often part of those deliberations, and overturning precedents as deeply ingrained as the court’s abortion jurisprudence would create outcry from the public, which has consistently said in polls that it favors Roe, as well as some restrictions on abortion rights.

Justice Brett M. Kavanaugh, who said during his confirmation hearings that Roe was “settled law,” indicated he was not persuaded that retaining the precedents was necessary or even wise.

He presented a long list of cases in which the Supreme Court had overturned past decisions, and said perhaps the best solution was for it to be “neutral” on an issue in which he said the Constitution is silent.

That would return the issue to the states, where some would effectively prohibit abortions and a majority would impose new and dramatic restrictions.

Solicitor General Elizabeth B. Prelogar, representing the Biden administration, said the restriction or even prohibition of abortion would be “severe and swift.”

“If this court renounces the liberty interests recognized in Roe and reaffirmed in Casey, it would be an unprecedented contraction of individual rights and a stark departure from principles of stare decisis,” said Prelogar, referring to the court’s tradition of respecting past decisions.

“The court has never revoked a right that is so fundamental to so many Americans and so central to their ability to participate fully and equally in society.”

The court’s liberals said the only thing that has changed since it found a fundamental right to abortion was the arrival of new justices.

“Will this institution survive the stench this creates in the public perception, that the Constitution and its reading are just political acts?” asked Justice Sonia Sotomayor. “If people believe this is all politics, how will we survive? How will this court survive?”

Justice Stephen G. Breyer, 83 and facing pressure from the left to retire so President Biden can appoint his successor, spoke at length, and read from the court’s decision in Casey, the first time there was a concerted effort to overturn Roe.

“To overrule under fire in the absence of the most compelling reason, to reexamine a watershed decision, would subvert the court’s legitimacy beyond any serious question,” Breyer read.

The dramatic day featured throngs of demonstrators outside the white marble court. Inside, because pandemic precautions have closed the building to the public, it was solemn and quiet.

Six lawyers, five of them women, sat in front of the justices. All were in black except for Mississippi Attorney General Lynn Fitch (R), who wore bright blue but left the argument to the state’s solicitor general, Scott G. Stewart.

Stewart said it was time for the court to acknowledge that Roe and Casey had not only failed to reach a compromise between protecting unborn life and ensuring female autonomy, they had inflamed the issue.

“They have no home in our history or traditions. They’ve damaged the democratic process. They’ve poisoned the law,” said Stewart, a former clerk to Justice Clarence Thomas. “For 50 years, they’ve kept this court at the center of a political battle that it can never resolve.”

But Julie Rikelman, a lawyer for the Center for Reproductive Rights representing Mississippi’s only abortion clinic, countered that turning the issue over to the states would allow legislatures to deny a woman a role in making one of the most crucial decisions she would ever face.

“For a state to take control of a woman’s body and demand that she go through pregnancy and childbirth with all the physical risks and life-altering consequences that brings is a fundamental deprivation of her liberty,” Rikelman said.

The court’s decision in Roe said women have a fundamental right to an abortion. Casey said there could not be prohibitions on abortion before viability and that regulations on the right could not impose an “undue burden” on a woman’s choice.

An abortion doctor from Kansas City, Mo., travels across state lines every month to provide care at clinics in the Midwest. (Whitney Leaming, Alice Li/The Washington Post)

Thomas, who joined the dissenting opinion in Casey nearly 30 years ago, that said Roe was wrongly decided, challenged the lawyers for the clinic and the federal government to locate a woman’s right to abortion in the Constitution.

“If I were to ask you what constitutional right protects the right to abortion, is it privacy? Is it autonomy? What would it be?” Thomas asked.

“It’s liberty, your honor,” Rikelman replied. “It’s the textual protection in the 14th Amendment that a state can’t deprive a person of liberty without due process of law, and the court has interpreted liberty to include the right to make family decisions and the right to physical autonomy, including the right to end a pre-viability pregnancy.”

Justice Samuel A. Alito Jr. also seemed ready to overturn Roe. After a long back-and-forth with Prelogar, the justice concluded: “So there are circumstances in which a decision may be overruled, properly overruled, when it must be overruled simply because it was egregiously wrong at the moment it was decided?”

But liberal Justice Elena Kagan disagreed, saying the court’s abortion jurisprudence did not fit such a scenario.

“Usually there has to be a justification, a strong justification in a case like this beyond the fact that you think the case is wrong,” she said. “And I guess what strikes me when I look at this case is that, you know, not much has changed since Roe and Casey, that people think it’s right or wrong based on the things that they have always thought it was right and wrong for.”

While Sotomayor in particular made impassioned remarks about the importance of abortion rights, the liberal justices were largely bystanders as the six conservatives debated what to do.

Kavanaugh and Barrett replaced two justices, Anthony M. Kennedy and Ruth Bader Ginsburg, respectively, who favored abortion rights.

Kavanaugh was the most outspoken among the three newest justices — and none of his remarks favored the abortion rights supporters. He rattled off a list of cases — involving on gay rights, integration, one-person, one-vote — that he said marked times when the court reversed previous decisions.

He repeated Mississippi’s argument that “the Constitution is neither pro-life nor pro-choice on the question of abortion but leaves the issue for the people of the states or perhaps Congress to resolve in the democratic process.”

If that’s the case, Kavanaugh said, and a justice believes the precedent is seriously wrong, “why then doesn’t the history of this court’s practice with respect to those cases tell us that the right answer is actually a return to the position of neutrality?”

Rikelman said being wrong was not enough. “There is no less need today than 30 years ago or 50 years ago for women to be able to make this fundamental decision for themselves about their bodies, lives and health.”

Barrett said one thing that had changed was a choice for women who did not want to take on the burden of parenthood. She noted that all states have “safe haven” laws that let women relinquish their parental rights after giving birth. 

“Why don’t the safe haven laws take care of that problem?” asked Barrett, who is the mother of seven, including two children who were adopted.

Rikelman replied that pregnancy itself “imposes unique physical demands and risks on women and, in fact, has impact on all of their lives, on their ability to care for other children, other family members, on their ability to work.”

In Mississippi, she said, it is 75 times more dangerous for women to give birth than to undergo a pre-viability abortion.

While much of the deliberations turned on whether to overrule the precedents, Roberts was especially intent on what he said was the issue the court had agreed to decide: whether all pre-viability prohibitions on elective abortions were unconstitutional.

He noted that Justice Harry Blackmun, who wrote the Roe opinion, had said in private papers that the viability line was arbitrary. He noted that many nations had restrictions on abortion in line with the Mississippi law.

But there was little support among the arguing lawyers, and little apparent interest from Roberts’s colleagues, for what seemed to be a suggestion for compromise.

Prelogar, Biden’s solicitor general, said viability was a principled place to draw a line, between conception and birth. If viability were removed, she said, the courts would face a continuing series of laws restricting abortion at earlier stages than 15 weeks.

But Roberts is fond of incremental steps when moving the law, and rewriting the court’s precedents to remove the viability line might become appealing as the justices deliberate the case.

The viability line has been cited across the country by judges who have struck down state prohibitions one after another that attempted to ban abortions earlier in pregnancy.

“In an unbroken line dating to Roe v. Wade, the Supreme Court’s abortion cases have established (and affirmed, and reaffirmed) a woman’s right to choose an abortion before viability,” Judge Patrick E. Higginbotham wrote for the U.S. Court of Appeals for the 5th Circuit majority that refused to allow the Mississippi law to take effect.

Mississippi passed the law in 2018. It would prohibit abortions after 15 weeks, with narrow exceptions for medical emergencies or severe fetal abnormality.

But to Prelogar’s point, the state also has a court-blocked law restricting abortions after six weeks of pregnancy, and a “trigger provision” that would practically eliminate abortion should Roe be overturned.

Exactly a month earlier, the court considered another abortion challenge, involving a unique Texas law that bans most abortions after six weeks of pregnancy and allows enforcement by private citizens.

That case is more procedural, and involves whether federal courts have the ability to stop such a law that runs against current constitutional protections for those seeking abortions.

The court has not yet issued a decision in the Texas case.

Wednesday’s case is Dobbs v. Jackson Women’s Health Organization.

Mariana Alfaro, Ann E. Marimow, Amy B Wang and John Wagner contributed to this report.