Sherif Girgis is an associate professor of law at Notre Dame Law School.

The question the Supreme Court agreed to decide in the Mississippi abortion case sounds deceptively simple: Are “all pre-viability prohibitions on elective abortions” unconstitutional?

If the answer to that is a clear yes, the justices will surprise us all and strike down the state law, which prohibits most abortions after 15 weeks. No one expects that to happen.

But if the answer is no, the justices will confront the reality that there is then no intellectually honest way for them to uphold the Mississippi law without overruling Roe v. Wade and Planned Parenthood of Southeastern Pennsylvania v. Casey, the 1992 case that reaffirmed the constitutional right to abortion.

There is, in other words, no middle ground in the pending case, Dobbs v. Jackson Women’s Health Organization. Upholding the Mississippi law without overruling the court’s previous abortion cases would lack support in any legal source, send even more abortion cases to the court and curb the justices’ ability to overrule Roe down the road.

The Roberts court, more lawyerly than those that decided Roe or Casey, looks to text, history and precedent. The Constitution’s text doesn’t mention abortion. And historically, by the time the 14th Amendment was ratified in 1868, a supermajority of states had banned abortion from conception.

That leaves precedent. But Roe and Casey forbid abortion bans — as opposed to modest regulations — at any point before a fetus is viable, around 24 weeks. To uphold 15-week bans, then, Dobbs must scrap precedent. Yet to retain some abortion right, Dobbs would need to draw a new line, allowing bans to start sometime before 15 weeks into pregnancy. When?

When a heartbeat begins? That criterion has no legal pedigree and comes when many are just learning they’re pregnant.

When fetuses feel pain? That may happen too late to justify the Mississippi law. Besides, it’s well established that states may not prevent exercises of fundamental rights to advance goals they could achieve by less restrictive means. So Dobbs can’t treat abortion as such a right and let states ban it to prevent pain they could also prevent by requiring fetal anesthesia, as some jurisdictions do.

Quickening, when women first feel the fetus move, around 14 to 17 weeks? One obstacle is that by the time the 14th Amendment was ratified, three-fourths of the states had authorized criminal convictions for pre-quickening abortions. Within 15 years, almost all others followed suit.

Even before pre-quickening abortions were criminalized, they faced other heavy legal burdens. So there was never a common-law right to abortion. That notion, central to Roe, has been debunked. Casey quietly abandoned it. “Quickening” is a nonstarter.

Could the court uphold 15-week laws such as Mississippi’s without drawing a new line? That would embolden states and sympathetic lower courts to embrace 12-, eight- or even six-week bans. The court might try to ignore the tumult, refusing to review challenges, but it can’t duck the issue for long. This dodge would prolong the politicization that the court wants to avoid.

Last try at upholding the law without overruling Roe and Casey: Some argue that Casey created two rules — one against pre-viability bans and another against laws imposing an “undue burden” on abortion access. They say the “undue burden” test merely requires leaving a meaningful window for aborting at some point. Under this theory, the court could abandon the viability rule (to save Mississippi’s law) while not endorsing or rejecting the “undue burden” test. Either way, 15-week laws would stand, as they leave ample time to abort.

But this suggestion badly misreads the “undue burden” test, which itself hinges on viability. Under Casey, what makes a regulation of the abortion procedure an “undue burden” is not that it leaves too little time for getting an abortion, but that it makes abortion too hard to get at a given point in time — any point until viability. Indeed, Casey said undue burdens were off-limits until viability for the same reason that bans were: “Before viability, the State’s interests are not strong enough to support a prohibition of abortion or the imposition of a substantial obstacle to” the procedure (emphasis added).

So if Dobbs declared instead that states need only leave some time to abort, it would end up reinforcing a constitutional right that the majority doesn’t believe exists. After all, the court wouldn’t be leaving part of Casey intact. It would be embracing something new to replace Casey’s test for abortion laws, as Casey replaced Roe’s.

And having justified a new abortion right in their own voices, the justices would have a hard time ruling later that there is no such right after all. That’s because they’d then be rejecting not only Roe and Casey but their own words in Dobbs. Why would the Roberts court take the heat for a decision in Dobbs that would only entrench a modestly slimmer abortion right?

That leaves one viable option for the justices who believe Roe and Casey were wrongly decided: to overrule them.