For more than two decades, many state legislatures have passed regulations making abortions increasingly difficult to obtain. Although Roe v. Wade is, theoretically, still a useful and necessary law, the Supreme Court allowed this trend to persist nonetheless—until now. In Whole Woman’s Health v. Hellerstedt, the Supreme Court struck down two provisions of a Texas statute that would have forced most of the state’s abortion clinics to close. The rhetoric in the majority opinion was more “policy wonk” than “ringing affirmation of women’s rights,” but this doesn’t make it any less of a feminist victory. This leads us to an important question. Why did Anthony Kennedy, the lone Republican appointee in the majority and the Court’s long-time swing vote on abortion, decide to find a regulation on abortion unconstitutional for the first time since 1992? The most likely answer is Kennedy’s feeling that Republican legislators have been undermining one of his most famous and important opinions.

A devout Roman Catholic personally opposed to abortion, Kennedy has always been an unlikely champion of reproductive rights. According to Edward Lazarus’s inside account of the case in Closed Chambers, when Planned Parenthood v. Casey came before the Supreme Court in 1992, Kennedy initially  agreed to provide the fifth vote therefore overruling Roe v. Wade. Soon after that, however, he changed his mind. He and his fellow moderate Republicans on the bench, Justices Sandra Day O’Connor and David Souter, crafted and signed a joint opinion in which they refused to overrule Roe, but modified the standard that would be used to evaluate abortion regulations. Under Casey’s rule, pre-viability abortions could not be banned outright, but regulating the procedure was constitutionally permissible unless these regulations constituted an “undue burden” on a woman’s right to choose.

Incidentally, the history of Casey provides evidence against one potential explanation for Kennedy joining Supreme Court liberals in Hellerstedt: the unexpected death of Antonin Scalia. We cannot know for certain if Scalia’s absence caused Kennedy to lilt to the left. But we do know that in 1992 Scalia—at the time a neighbor of Kennedy’s in suburban Virginia—spent many fruitless hours trying to persuade Kennedy to change his mind. The fact that Kennedy is ideologically moderate does not mean he is also susceptible to bullying, and I believe with near certainty that, had he lived, Scalia would have written a blistering dissent in this case.

In theory, the “undue burden” standard could provide robust protection for abortion rights, but in practice, prior to Monday’s decision, it didn’t. And one reason for this is that Kennedy believed that his fellow justices had reneged on his carefully constructed compromise in Casey.

In the 2000 case Stenberg v. Carhart, a 5-4 Court struck down Nebraska’s ban on so-called “partial-birth” abortion. For reasons concisely summarized by Justice John Paul Stevens in his concurrence, I believe this decision was correct. But Kennedy believed he had been double-crossed by his fellow justices, especially Justices O’Connor and Souter. In a lengthy and uncharacteristically angry dissent, Kennedy repeatedly lamented the Court’s “basic misunderstanding” and “misinterpretation” of Casey.

After Justice O’Connor’s replacement by Samuel Alito, Kennedy had the chance to restore his own interpretation of Casey, and wrote an opinion in the 2007 case Gonzales v. Carhart upholding a federal ban on “partial birth” abortions. Even more disturbing was the fact that Kennedy’s opinion embraced the pseudo-scientific justifications offered by opponents of legal abortion to support his decision. Kennedy made it clear that he would be very deferential to abortion regulations in the form of health regulations, no matter how little the regulations had to do, in practice, with protecting women’s health.

Many state legislatures got the message and passed an increasing array of regulations, the most insidious of which were targeted regulations of abortion providers (TRAP). TRAP laws resembled medical regulations, but their real purpose, in singling out abortion clinics despite the relative safety of the procedure, was to create burdens for these clinics, making it difficult or even impossible for them to operate. Texas HB2, an issue of contention in Hellerstedt, is a classic example. Texas placed requirements on facilities and doctors that would have closed more than half of the states’ already relatively small number of clinics, regardless of actual safety concerns.

It was this sort of practice that almost certainly pushed Kennedy back toward the liberal faction of the Court. Facing a brutal interrogation at oral argument, the medical justifications offered by Texas Solicitor General Scott Keller were almost farcically thin. It’s telling that the dissenting opinions in Hellerstedt focused primarily on procedural questions, and offered only cursory and half-hearted attempts at defending the sham justifications offered by Texas in support of its statute. The Texas regulations are not about protecting women’s health. They’re about trying to restrict, and eventually eliminate, abortion access.

And unlike in Carhart II, not only were the justifications weak, the effects were broad-ranging. Nobody with any commitment to reproductive rights could overlook a statute that shut down large numbers of clinics based on alleged medical justifications that (as Justice Breyer’s opinion showed in painstaking detail) were an insult to citizens’ intelligence. If Kennedy thought liberals were being untrue to Casey during its first decade, it was now being undermined by conservatives. Republican legislators were in fact using Casey to eliminate the rights Casey sought to protect, and it’s not surprising that Kennedy refused to go along.

Plenty of objections can be launched at Casey from both the left and right, and rightfully so. But it’s clear that Kennedy takes the compromises in this decision very seriously. It’s not surprising that state legislatures took his previous opinion as a green light to attack abortion rights, but it’s also not surprising that the pendulum is now swinging back. By demanding that state legislatures provide real medical justifications for regulations that substantially restrict abortion access, the Court has restored needed teeth to Roe. Kennedy’s past deference to anti-abortion interests has now turned to skepticism, and, for supporters of reproductive rights, this is excellent news indeed.