Then there is the broader issue of social consensus. The continuing nationwide division over same-sex marriage, notwithstanding the recent shift in public opinion, might give Chief Justice Roberts pause. He may find it unwise to put the Supreme Court’s blessing on a legal rule that would create so much uncertainty for so many people in such a bedrock institution.

Conservatives often see variation across state law as a good thing, a point Justice Louis D. Brandeis noted in his famous dissenting opinion heralding states as laboratories of experimentation. But conservatives might also question the utility of watching the country descend into a protracted debate on so basic a matter as family formation, with red states pitted against blue, for another generation.

As chief justice, Mr. Roberts occupies a unique place in the judiciary. While it is not his job to simply validate the decisions of the lower court judges — the Supreme Court should reverse the lower courts when they err — having faith in the lower federal judiciary, and showing respect for the dialogue between the Supreme Court and lower federal courts, might be especially appropriate here.

Since the 2013 Windsor ruling, four federal appellate courts and more than 30 federal trial judges have issued pro-marriage rulings for same-sex couples. (By contrast, only one federal appellate court — the Sixth Circuit, based in Cincinnati — and a handful of federal trial judges have ruled against same-sex couples.) These judges reflect a broad array of appointees by Republican and Democratic presidents alike. Does Chief Justice Roberts truly believe that so many of his lower-court colleagues have gotten the law wrong? Possibly — but the growing consensus on the ground could nudge him to side with a vast majority of his colleagues on the federal bench.

The states will argue that courts should not interfere with their sovereign power to decide certain questions of marriage policy or curtail the policy debate. Both arguments generally appeal to conservative jurists. But the court may decide that a uniform rule favoring same-sex couples would be the more prudent and moderate outcome.

In short, the posture of these cases, their significance in the broader history of the Supreme Court, and their administrative and practical implications are likely to give the chief justice pause before voting against the right to marry. If Chief Justice Roberts focuses on these questions, his vote should be with the plaintiffs this time around.