In previously navigating a way to uphold the Affordable Care Act, Chief Justice Roberts had given every indication that he was worried about the court’s image.

He acted similarly last week in joining the four justices nominated by Democrats in writing an opinion that sent back to a lower court a politically inflammatory case about whether to add a question about citizenship to the coming census. The question is viewed as a backdoor effort by the Trump administration to undercount minorities and dilute their political influence.

Chief Justice Roberts seemed to recognize that allowing the court to deliver two major political victories for Republicans would have fueled increasing Democratic mistrust of the Supreme Court. But in trying to maintain the court’s reputation — however tarnished — of judicial nonpartisanship, he underscored just how political the court has become.

The chief justice’s efforts to steer the court through partisan shoals is likely to get even more difficult as the justices are called upon to referee hot-button issues left unaddressed by partisan dysfunction in Congress and the White House.

Complicating his task is the fact that the other four conservatives — Justices Gorsuch, Kavanaugh, Clarence Thomas and Samuel A. Alito Jr. — seem to be forming a power center not easily influenced by the chief justice. If President Trump were able to replace one of the remaining liberals on the court, it would fortify a conservative majority that would not need the chief justice’s vote. And Democrats, with the changes in nomination rules imposed by both parties over the past six years, would have no power to stop it.

All of this makes this moment seem particularly perilous for the court. Though it has long been held in higher esteem than the other two branches, a growing number of Americans see it as infected by partisanship — and are questioning its legitimacy. In the eyes of many, Democrats in particular, the stonewalling of Judge Garland that led to Justice Gorsuch’s nomination and the accusations of sexual misconduct against Justice Kavanaugh have tainted both men’s confirmations.

As has long been noted, the Supreme Court has no army to enforce its rulings. Its legal — and moral — authority stems almost entirely from the willingness of Congress, the president and the American public to accept its decisions. What might happen if that authority dissipates?