WASHINGTON (CN) — In the most consequential abortion case to come across the high court’s docket in decades, Chief Justice John Roberts stood alone Wednesday as he tried to convince his colleagues to chip away at the constitutional right to abortion without burning the whole thing to the ground.

The conservative Bush appointee has been often voted with his liberal colleagues and is known to want to preserve the legitimacy of the court as an impartial judicial institutional and not a bench of partisan jurists. While some of his conservative colleagues seemed eager to overturn the almost 50 year precedent of Roe v. Wade, Roberts repeatedly tried to convince them to take a softer approach.

The heart of Roberts’ arguments hung on the idea that the viability line of a fetus — its ability to survive outside the womb — was arbitrary and could be replaced.

“Viability, it seems to me, doesn’t have anything to do with choice,” Roberts said.

The court held that women had the right to abortion with the 1973 decision in Roe, but states could limit that right after the second trimester. It would later reaffirm the right to abortion in the 1992 case Planned Parenthood v. Casey while changing the states’ right to intervene at the viability of the fetus instead of according to trimesters. The viability line currently stands around 23 or 24 weeks.

Roberts on Wednesday drew from the writings of Justice Harry Blackmun — who wrote the opinion in Roe — to say the precedent’s author didn’t even believe the viability line was central to the right.

“In fact, if I remember correctly, and I — it’s an unfortunate source, but it’s there — in his papers, Justice Blackmun said that the viability line was — actually was dicta,” Roberts said. “And, presumably, he had some insight on the question.”

Roberts’ line of questioning reflects a theme the country has seen before from the chief justice.

“The comments of the chief justice reflect the concern that the Supreme Court should help hold the country together rather than tear it apart,” Richard Bernstein, an appellate lawyer, said in a phone call.

While defending Mississippi’s Gestational Age Act  — which bans all abortions after 15 weeks — Mississippi Solicitor General Scott Stewart asked the court to overrule Roe and Casey but he also attacked the viability line.

“Roberts was alone in examining a narrower argument that Mississippi has made — there have been two arguments, one that the court should overrule Roe and Casey entirely, and two, the court should overrule what the court has called kind of a core part of Roe that before viability, that states can’t ban abortions,” said David Gans, director of the human rights, civil rights, and citizenship program at the Constitutional Accountability Center. 

Besides quoting Blackmun, Roberts also picked at the idea that, if the viability line is an arbitrary standard, then why couldn’t the court just draw the line somewhere else.

“If it really is an issue about choice, why is 15 weeks not enough time,” Roberts asked.

In this way, Roberts floats getting rid of the viability line without having to overturn Roe. One of the possibilities for a ruling in this case — which will not likely be seen until June or July — would be nixing the viability line and replacing it with something else.

“I think one of the difficulties of Roberts’ approach is the question of what would replace the viability line,” Gans said. “Mississippi couldn’t offer something that would take the place of viability. That leaves the law at sea.  If the line isn’t viability, and it’s not 15 weeks — because that’s where Mississippi’s ban is — is it 10 weeks, is it six weeks? It would be anathema to principled judicial decision making to throw out 50 years of precedent based on viability without saying what the line is.” 

Not only will Roberts and the other justices have to decide on where to draw that line if they were to rule in this way, but they would have to find a justification for it. Mississippi did not offer any arguments for why 15 weeks specifically would be better than viability whereas the viability line has an established justification.

“There are logical and biological justifications for having the point of viability — the point at which the fetus can survive outside the womb can survive outside the pregnant person — as the line to be drawn here,” Meagan Burrows, staff attorney with the ACLU Reproductive Freedom Project, said in a phone call. “So there was justification for it and so it is grounded in some logic and is objectively verifiable, it is medically verifiable by a medical professional, by a doctor, and it doesn’t leave to the court … the task of resolving where to move this line.”

If the court decided to gut the viability line without providing a replacement for it, it could lead to a tsunami of cases as states try to determine how to regulate abortions.

“You could have a scenario in which the court simply got rid of the viability line and said Mississippi’s ban was valid but didn’t replace that with another line,” Gans said. “That would produce a wealth of new abortion bans that would test where that line would be.” 

A problem for overturning Roe cited by the abortion providers attorney, the U.S. solicitor general, and liberal justices on the court is it would violate stare decisis — the doctrine that obligates courts to look to precedent when making decisions.

“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,” U.S. Solicitor General Elizabeth Prelogar said. “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.”

Stare decisis seemed to be what was holding Roberts back from fully embracing Mississippi’s request to overturn Roe.

“​The justices, including Justice Roberts, really care about the institutional integrity of the court and I think certainly stare decisis is one of the principles that inform and bolster that integrity so I do think that is certainly at play here,” Burrows said.

But even with the conservative justices looking to completely overturn Roe and their liberal colleagues wanting to shoot down Mississippi’s law, a ruling along the lines of Roberts’ questioning would be anything but moderate.

“I would caution against viewing a ruling that eliminated the viability line as a moderate outcome,” Gans said. “A ruling that overruled what is key linchpin to Roe and Casey and allowed states to ban abortions at 15 weeks would be hugely consequential … the position that Roberts seemed interested in would still be a huge change in the law that would cut off basic fundamental rights for many persons.” 

Getting rid of the viability line could effectively overturn the rights protected by Roe without explicitly overturning the ruling.

“To say you’ve gotten rid of viability but you haven’t overruled Roe smacks of dishonesty, it feels like you’re not really being upfront about what you’re doing,” Gans said.  

An anti-abortion lobbying organization, Texas Alliance for Life, used the same argument as Roberts to push for Roe to be overturned completely. In their view, if the viability line is arbitrary, then Roe should be thrown out completely.

“The question they were considering is not whether a 15-week ban is constitutional, but rather any attempt to protect unborn babies from abortion prior to viability is constitutional,” said Joe Pojman, executive director of Texas Alliance for Life. “So if that points to the direction everybody understands … I guess one way to read this, and this is how we’re looking at it, it’s come down to this it’s very high stakes either Roe v. Wade stays or Roe v. Wade is overturned in whole.”

The right to abortion is not the only constitutional right at play here either. If the court were to overturn Roe, other rights based on the same principles could be at risk.

“I think one of the big questions in this case is to what extent does the 14th Amendment protect rights that are not enumerated in the Constitution, and I think many of the conservatives on the court take the view that protecting unenumerated rights is borderline illegitimate,” Gans said. 

The justices specifically cited Griswold, Lawrence and Obergefell as being in danger.

“We’re really at a crisis point here … unraveling the right to an abortion which has for decades been deeply grounded in the substantive due process and judicial doctrine also leaves exposed other important rights that are similarly grounded in substantive due process and liberty and privacy, such as the right to contraception, the right to marry who we choose, the right to form families in the way that we choose,” Burrows said. “I think all of those are left exposed and are left potentially next to be on the chopping block if this court does an about face with respect to the right to abortion and overturns 50 years of precedent protecting it.”