In 2011, Chief Justice John G. Roberts, Jr., used his annual report about the state of the federal judiciary to defend the probity of his Court colleagues. He was responding to members of Congress, experts in legal ethics, and legal advocacy groups who wanted the Court to be subject to the Code of Conduct for United States Judges, which applies to all other federal judges.

In the previous decade, a few of the Justices had not recused themselves from cases despite persistent doubts about their ability to decide them impartially. Most dramatically, Justice Antonin Scalia had rejected a motion that he recuse himself from a case that provided a textbook example of the circumstances a Justice should avoid.

Scalia’s close friend Dick Cheney, who was then the Vice-President, was accused of lying about the composition of a White House group that was setting national energy policy. While the case was pending, Scalia and Cheney went duck hunting together, and Cheney gave Scalia and two of his family members a ride on a government Gulfstream jet from Washington, D.C., to Louisiana, where they did their hunting.

Scalia eventually joined the majority of the Court in a procedural ruling that sent the case back to a lower court. But he was also the only Justice to join a separate opinion by Justice Clarence Thomas saying that the activities of the Vice-President should not be scrutinized in litigation run amok.

If Scalia had been a member of the United States Court of Appeals for the District of Columbia Circuit, as he was before becoming a Justice, it would not have been up to him to decide whether he should be recused. Under the code of conduct, the chief judge for his circuit would have considered any motion calling for Scalia’s recusal, conducted an inquiry, and resolved the matter.

As Roberts explained in his report, the code of conduct does not apply to the Justices because of “a fundamental difference between the Supreme Court and the other federal courts.” The Constitution created the Supreme Court and gave Congress the power to establish lower federal courts. To set policies for those courts, including about recusal, Congress established a group of federal trial- and appeals-court judges called the Judicial Conference, and made the Chief Justice the presiding officer.

“Because the Judicial Conference is an instrument for the management of the lower federal courts, its committees have no mandate to prescribe rules or standards for any other body,” Roberts wrote. “The Justices follow the same general principles respecting recusal as other federal judges, but the application of those principles can differ due to the unique circumstances of the Supreme Court.”

Lower-court judges are required to obey the principles. The Justices follow them, but they are not obligated to obey them. As a result, the Justices of the Supreme Court are the only judges in the United States who are not bound by a formal, full-blown ethics code.

Since the seventeenth century, a fundamental axiom of Anglo-American law has been that “no man shall be a judge in his own case.” In matters of judicial ethics, however, each Justice is precisely that. Their sometimes questionable decisions in these cases are an important reason why the Court’s standing in American life has declined notably since 2000.

Last week, the Times’ Andrew Ross Sorkin wrote about the 2014 ABC v. Aereo decision, in which the Court effectively shut down Aereo, a television streaming service, by holding that it violated the copyright of broadcasters when it captured their signals on small antennae and provided their programming to paying subscribers. With newly disclosed financial information from the Chief Justice, Sorkin reported that, when Roberts voted in favor of the broadcasters, he owned as much as five hundred thousand dollars of stock in Time Warner, which filed a friend-of-the-court brief supporting the industry position.

The Chief Justice and Justices Stephen Breyer and Samuel Alito, Jr., each own substantial amounts of stock in individual companies. (Their colleagues own exchange-traded funds, index funds, retirement accounts, or pensions, which are invested in, among other things, more than one publicly traded company, and don’t have the same potential for creating a conflict of interest.)

According to the advocacy group Fix the Court, between 2009 and 2014 Roberts, Breyer, and Alito voted in thirty-seven cases where a company in which they owned stock filed a friend-of-the-court or amicus brief. They voted in support of the position the company advocated twenty-seven times— seventy-three per cent of the cases. Fix the Court reported that it “did not find a single instance in which a justice made the decision to recuse due to an amicus-based conflict.”

Like Scalia, each of those Justices was once on a federal appeals court, and bound then by the code of conduct. There is not much ambiguity about what that means in situations like these. The Judicial Conference publishes formal opinions on ethical issues that come up frequently for judges. Advisory Opinion No. 63 deals with “Disqualification Based on Interest in Amicus that is a Corporation.” Based on this opinion, it seems likely that, if the Justices had been on appeals courts considering those cases, they would, in at least some of them, have been recused because of an amicus-based conflict.

As the opinion explains, “Any interest that could be substantially affected by the outcome of a proceeding is a disqualifying interest; this restriction applies to an ownership interest in any corporation, whether or not the corporation appears as an amicus.” It goes on to say that “under the Code the extent of the judge’s interest is irrelevant.”

Louise Slaughter, a congresswoman from New York, co-authored a bill called the Supreme Court Ethics Act, which was reintroduced this year. Its purpose, she explained in a law-review article, was to require the Court to “adopt clear, written rules that establish standards by which justices’ behavior can be guided and assessed by both themselves and the American people.”

In proposing that the Court impose rules on itself, Slaughter and some others accept the Chief Justice’s argument that there is a fundamental difference between the Supreme Court and other federal courts, and that its unique circumstances support exempting the Justices from obeying the code of conduct. That is debatable: the Court observers to whom Roberts responded see no problem with Congress applying the code to the Justices.

But even if Slaughter is correct that the Court should adopt its own set of rules, which could be the code of conduct tailored to the unique circumstances of the Court, that approach has the problem of emphasizing the Court’s isolation rather than its prominence. It overlooks the highly visible and primary role that the Court and the Justices have as exemplars for state and local courts, and for judges throughout the country.

Judges are elected in thirty-nine states, and there is plenty of potential for them to have conflicts of interest: lawyers are primary donors to their campaigns, and it is common for lawyers to appear before judges they have supported. The issue of when a state or local judge should be recused from deciding a case is of such wide concern in the states, especially in those with judicial elections, that the American Bar Association undertook a major study about it. The solution, the A.B.A. study concluded, was for a judge not to rule on a motion for his recusal. Otherwise, judges who judged their own cases would continue to undermine their own credibility and public confidence in courts.

The study dealt only with state courts, but the logic of this central recommendation applies to federal courts as well, and the code of conduct for lower federal courts incorporates this way of thinking. If the Court does not recognize and act on this insight, it will continue to undermine its standing with the public and provide a lamentable model for state and local judges across the country to do the same.

Impartiality is an essential requirement for a judge. But, as Charles Geyh, the legal scholar who directed the A.B.A. study, wrote, “It is not enough that judges be impartial; the public must perceive them to be so.” Whether a judge is on the highest court in the land or on one of the many others, we are much more likely, in a case where his impartiality has been questioned, to view him as impartial if another judge concludes so after conducting an independent appraisal. That’s crucial to the effectiveness of this country’s courts, which makes it crucial to the soundness of American democracy.