Chief Justice John Roberts shocked court watchers by siding with the liberal wing of the bench in a decision that blocked a restrictive Louisiana abortion law from going into effect.
But he also set up a potential showdown over abortion next year, in the thick of the 2020 presidential campaign.
In an unusual after-hours order Thursday night, the conservative Roberts joined the court's four Democratic appointees in granting a stay of the Louisiana law. Reproductive-rights activists argued that the law would cripple abortion access in the state. The high court had found a similar law unconstitutional in Texas three years ago, in a case in which Roberts dissented.
The law required abortion doctors to have admitting privileges at a hospital within 30 miles of their clinic, which would have left only one provider in a state with a population of nearly 5 million, according to the plaintiffs.
The decision to block the law was temporary. That means that the upshot of the justices' 5-4 vote granting a stay, issued without a ruling on the merits, is a likely battle over the court's abortion rights precedents during the most heated months of the 2020 presidential election next year.
The court is now expected to take up a formal petition from the Center for Reproductive Rights, which represented two abortion doctors and a clinic in the case, to hear arguments on the matter in its term beginning in October.
A decision would likely be handed down around the end of the term in June 2020, a month before Republicans and Democrats host their national conventions.
There is some recent precedent for Supreme Court decisions providing fodder to presidential contenders.
In June 2012, the justices handed down their landmark decision upholding the Affordable Care Act, for instance. Roberts, who was appointed by President George W. Bush, sided with the liberals to narrowly uphold President Barack Obama's signature domestic policy achievement.
Nine years earlier, the court made waves by stepping into LGBT rights a year before the presidential contest between Bush and John Kerry.
"In 2003, it wasn't a presidential election year, but it was close enough, and the court's decision in Lawrence v. Texas was used very powerfully by those in the conservative movement to mobilize voters," said Michael Dorf, a law professor at Cornell University, referring to the case that outlawed bans on sodomy nationwide. "There is not a bad argument that it was used to get Bush elected."
Just months after the court handed down its decision protecting gay rights, Bush called for a constitutional amendment that would have defined marriage as between a man and a woman.
The Democrats vying for their party's 2020 nomination so far have taken strong positions defending reproductive rights. In recent weeks, President Donald Trump has made clear that he intends to make abortion a major issue. The Supreme Court, which typically tries to avoid the glare of partisan politics, could find itself right in the thick of it.
That could be bad news for reproductive-rights activists, who have warned for months that the high court's abortion precedents are unlikely to withstand the addition of Trump's two nominees, Justices Neil Gorsuch and Brett Kavanaugh.
Leana Wen, president of Planned Parenthood Federation of America, said in a statement Wednesday that it was "increasingly likely" that the landmark abortion ruling Roe v. Wade could be overturned.
And even if Roe, which made abortion legal nationwide, is not overturned, a ruling on this case in favor of Louisiana could be nearly the same as if it had been, warned Jen Dalven, director of the ACLU's Reproductive Freedom Project.
"For thousands of women, the result would be exactly the same as if you overturned Roe v. Wade," Dalven said. "It's a sneaky, stealthy way to deny abortion access for thousands and thousands of women without having to get that headline."
Thursday night's vote was the first time that Trump's two nominees had to address their views on abortion since their Senate confirmation hearings. During those hearings, Kavanaugh and Gorsuch said they viewed Roe as settled law.
In a move that alarmed civil rights groups, both men said Thursday that they would have allowed the Louisiana law to take effect.
Gorsuch joined his fellow conservatives, Justices Clarence Thomas and Samuel Alito, in saying he would have permitted the law to take effect as soon as Friday. Kavanaugh agreed, but wrote separately that he would be open to reconsidering the legality of the law if the dire warnings from abortion rights groups materialized.
Kavanaugh's dissent had noted similarities to his only previous decision on abortion, issued while a federal appeals court judge in Washington, Dalven said. That decision, which was ultimately overturned, would have delayed a pregnant 17-year-old immigrant from obtaining an abortion.
Dalven said Kavanaugh had now twice effectively voted to block abortions while cloaking the decision in technical reasoning.
"I can't look into his mind to understand the intention behind it, why he's doing it that way, but the effect is the same," she said.
Cornell's Dorf said he expected that if the court does decide to review the law next term, the justices are likely to take a page out of Kavanaugh's playbook. He said they could likely find specific, technical grounds to find the Louisiana law constitutional without expressly overturning their own 2016 precedent on the similar Texas law.
"There is an argument by some in the pro-choice community that this is the worst of all possible worlds," Dorf said. He said that outcome could leave in place the "illusion of an abortion right," without generating the type of headlines that would energize liberals.
"I think that is a real concern, but I don't think that it's as bad as explicitly overruling [Whole Women's Health]. You can lose by winning, but it's usually worse to lose by losing," he said.