(Bloomberg Opinion) -- Chief Justice John Roberts has drawn his line in the sand.  In what may well come to be his most famous opinion ever, a solo concurrence in today’s Louisiana abortion case, Roberts voted to uphold Casey v. Planned Parenthood, the 1992 decision in which Justices Anthony Kennedy, Sandra Day O’Connor, and David Souter declined to overturn Roe v. Wade. The basis was stare decisis — the doctrine of precedent which, he said, instructs us “to treat like cases alike” rather than changing the rules and reversing course.

Roberts made it clear that he reads the Casey decision very narrowly, to allow restrictions on abortion that don’t impose an “undue burden” on reproductive freedom. He signaled that he is still open to upholding laws that chip away at the existing abortion rights framework, which has been his approach in the past. Roberts hasn’t had some transformative epiphany that made him into a staunch defender of abortion rights.

But crucially, Roberts also made it as clear as he could that, so long as he is the swing vote on the court, he isn’t open to overturning Roe or Casey. He doesn’t want the Roberts Court to be remembered as a reactionary body that reversed nearly 50 years of settled law on abortion rights.

This is a massive setback for legal conservatives. It means that to overturn Roe and Casey, they need President Donald Trump to be re-elected and to get at least one more conservative on the court to replace a liberal justice.

If Trump is not re-elected, then Roberts has single-handedly pulled off what the troika of Kennedy, O’Connor and Souter did almost thirty years ago: saving abortion rights for another generation.

Roberts’s decision in today’s case, June Medical Services v. Russo, began with his acknowledgment that the Louisiana law in question was basically identical to the Texas law that the Supreme Court struck down in 2016 in a case called Whole Woman’s Health v. Hellerstedt. In that case, Kennedy provided the fifth vote for a strikingly liberal decision by Justice Stephen Breyer, who wrote the plurality opinion for the court in today’s case.

The Louisiana law, like the Texas law, imposes a set of restrictions on abortion providers that include requiring doctors have admitting privileges at a hospital no more than 30 miles away from the abortion clinic. In the Hellerstedt case, Breyer took the “no undue burden on abortion rule” laid down in the Casey decision and turned it into a cost-benefit analysis. (Breyer made his academic career as a scholar of regulation, and cost-benefit analysis is in his blood.)

Roberts joined the dissenters in the 2016 Hellerstedt case. You read that right. Four years ago, Roberts thought the Texas restrictions were consistent with Casey. His vote at the time was based on the strategy that he had long embraced of not overturning Roe but instead subjecting abortion rights to death by a thousand small cuts.

Today, Roberts did not say he had changed his mind. Rather, he forthrightly explained that the doctrine of precedent attached to the 2016 decision, and that he would not overturn it. By extension, Roberts affirmed that he considers the doctrine of precedent to apply to Casey, on which the Hellerstedt decision was based. By affirming the 2016 president, he reaffirmed the 1992 precedent.

Along the way, Roberts pretty thoroughly gutted the Hellerstedt decision, with its innovative application of cost-benefit analysis to abortion law. He stated that the true holding of the Hellerstedt case was nothing but an application of the old Casey undue burden test.

Since Roberts’s vote is required for this or any near-term decision striking down any law that burdens abortion, his version of Casey, and of the 2016 decision, is now the only one that matters. Breyer, joined by the liberals, restated much of his previous opinion. But that doesn’t matter without a fifth vote, which they can only get from Roberts — unless Joe Biden becomes president, controls the Senate, and gets to replace one of the conservatives with a liberal, so that Roberts is no longer the swing vote.

What all this means is that, to some degree, we are going back to the way things were between 1992 and 2016. There is no conservative majority on the court to overturn Roe or Casey. There is, however, a swing voter — now Roberts — who will consider on a one-by-one basis state laws that restrict abortion rights. If Roberts says those laws don’t impose an undue burden, they will survive. If he thinks they do, the laws will be struck down.

And Roberts is suggesting that he will be even more willing to allow such laws to remain in place than was Kennedy at the end of his career. In practice, therefore, abortion rights will remain under threat. There will be lots of work for the pro-choice movement.

At the level of principle, however, the pro-life forces have been once again defeated at just the moment when total victory seemed possible — just like what happened after Ronald Reagan appointed Kennedy and O’Connor and George H.W. Bush appointed Souter.  It’s not so much that the pro-choice side won over Roberts as that the pro-life side lost him. 

Roberts now permanently enters the pantheon of judicial conservatives who moved to the center on the Supreme Court. His commitment to stare decisis, leaving precedent in place, turns out to be great enough to lead him to a decision that will be long reviled by conservatives.

In my line of work, we call that principle.

This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

Noah Feldman is a Bloomberg Opinion columnist and host of the podcast “Deep Background.” He is a professor of law at Harvard University and was a clerk to U.S. Supreme Court Justice David Souter. His books include “The Three Lives of James Madison: Genius, Partisan, President.”

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