If you’ve only casually followed the law and politics of the abortion issue in recent years, you may wonder why there’s so much activity and controversy when the basic constitutional law of reproductive rights hasn’t really changed. But as Jeffrey Toobin explains in a wonderfully succinct column at The New Yorker, it has changed in subtle ways, mainly because its most recent formulation–Sandra Day O’Connor’s prohibition of abortion restrictions that pose an “undue burden” on the right to choose prior to fetal viability–is capable of being turned inside out.

[T]he key phrase did not have a fixed, self-evident definition. And as the Court moved to the right, following O’Connor’s resignation, the scope of the constraints on state power began shrinking. In 2007, the year after Samuel Alito replaced O’Connor on the Court, Justice Anthony Kennedy wrote, for a 5-4 majority, the decision in Gonzales v. Carhart, which upheld Congress’s ban on so-called partial-birth abortion. Kennedy quoted O’Connor’s language from Casey, in which she defined an “undue burden” as existing when the “purpose or effect [of the regulation] is to place a substantial obstacle in the path of a woman seeking an abortion before the fetus attains viability.” But then Kennedy went on, essentially, to ignore that definition, since he was approving a law that disallowed what was then the most common form of second-trimester abortion.

The decision in Carhart was followed, in 2010, by landslide Republican legislative victories that brought several state governments under the full control of the G.O.P. In virtually all of these states, and in several others that were already in Republican hands, politicians sought to make obtaining an abortion even more difficult. In Texas, this meant the passage of a law that required abortions to be performed in ambulatory surgical centers, which are more or less miniature hospitals. There were already only forty-one abortion clinics in the state, for a population of five million women of reproductive age, and more than twenty were forced to close because of the new requirements; when further restrictions went into effect, the state was on the verge of being left with only a half-dozen clinics, and none at all in the Rio Grande Valley. This was the very definition of an undue burden—a law whose “purpose or effect” was “to place a substantial obstacle in the path of a woman seeking an abortion.” In August, a courageous federal district-court judge in Austin, Lee Yeakel, reached just that conclusion and held that the new provisions violated a woman’s right to terminate her pregnancy. “The ambulatory-surgical-center requirement is unconstitutional because it imposes an undue burden on the right of women throughout Texas to seek a previabilty abortion,” Yeakel wrote in response to a lawsuit brought by the Center for Reproductive Rights on behalf of abortion providers.

Nonetheless, the Texas law has been upheld by the conservative Fifth Circuit Court of Appeals.

[T]he members of the Fifth Circuit panel seem to believe that anything short of a nationwide ban on abortion does not amount to an undue burden on women’s rights. This is the argument that will soon be heading to the Supreme Court. Will the Court’s conservatives—who appear to have, with the addition of Anthony Kennedy, a one-vote majority on this issue—define the “undue burden” test into meaninglessness? Or will they junk the test altogether and give states an even freer hand to restrict abortion rights? O’Connor has been gone from the Supreme Court for nearly a decade. The question, now, is whether her great achievement will soon be gone, too.

It’s entirely possible SCOTUS will radically restrict abortion rights while blandly insisting (outside fiery concurrences from Scalia and Thomas) it’s not challenging precedents at all. That’s how quiet judicial revolutions–and counter-revolutions–play themselves out.

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Ed Kilgore is a political columnist for New York and managing editor at the Democratic Strategist website. He was a contributing writer at the Washington Monthly from January 2012 until November 2015, and was the principal contributor to the Political Animal blog.