Supreme Court Chief Justice John G. Roberts Jr. (Mark Humphrey/AP)

ROE V. WADE and subsequent Supreme Court precedents stand for the proposition that a woman has a constitutional right to choose abortion, subject only to federal and state regulations that do not impose an “undue burden” on that right. At a time when Americans distrust all branches of their federal government, the Supreme Court’s legitimacy challenge can be stated as a question: Will a court with a five-justice conservative majority, appointed by Republican presidents hostile to Roe, move swiftly to strike down, or hollow out, that well-established precedent?

After Thursday, there was a new reason to hope the answer might be “no.” One of those five conservatives, Chief Justice John G. Roberts Jr., joined with four pro-Roe Democratic appointees to block enforcement of Louisiana’s abortion-clinic law, pending consideration of the law’s opponents’ request for a full review of the law by the high court.

The opponents’ case is strong. Louisiana’s law requires abortion clinics to be staffed by doctors with admitting privileges at a hospital no more than 30 miles away. The Supreme Court struck down a similar Texas statute in 2016, holding that its purported benefits to women’s health did not outweigh the closure of many abortion clinics it would cause — thus creating an undue burden on the right to choose. That is now binding precedent on all lower courts, including those in Louisiana, whose handful of clinics say the law would shut most of them. Nevertheless, a sharply divided New Orleans-based federal appeals court upheld the Louisiana law.

Mr. Roberts disagreed with his newest colleague, Justice Brett M. Kavanaugh, whose dissenting opinion recommended, essentially, that the court let the statute take effect to see if it would, indeed, restrict abortion excess as much as opponents predict. They could return to the Supreme Court if and when that happened, Mr. Kavanaugh maintained. The flaw in this ostensible compromise is that it imposes the risks of delay on the abortion clinics and their clients, even though the controlling precedent, the court’s 2016 ruling against the Texas statute, is in their favor.

By granting opponents of the law a chance to defeat it before it takes effect, Mr. Roberts fairly allocated risk — but hardly forecast the outcome. His own views on the underlying undue burden issue are not entirely clear. He voted against challengers to the Texas law in 2016, but the dissenting opinion by Justice Samuel A. Alito Jr. that Mr. Roberts joined focused on procedural issues. The chief justice and his fellow members of the 5-to-4 majority Thursday provided no written opinion. The Supreme Court rule pursuant to which they granted a stay, however, suggests that all five of them see a “fair prospect” that opponents of the Louisiana law will, in the end, win their case.

In short, the chief justice has shown that if, indeed, abortion law is about to be changed, it won’t be without a hearing at the Supreme Court. Even if the challengers lose, therefore, Thursday’s decision promotes the judiciary’s legitimacy.