It gives an unelected public official immense power for decades over the lives of hundreds of millions of people without any accountability. It should be abolished and replaced with a single, nonrenewable term of approximately 15 years.

The justices are among the most powerful people on the planet. Their mandate reaches into every corner of American life — and even abroad. Much of the time, they operate in secrecy — some of it necessary, but in many respects not. They are treated with enormous respect, even awe, yet their lives are largely isolated from those they influence, making it hard for them to understand what most people deal with.

They can remain in office until they die or choose to leave. Congress has also given the justices virtually complete control over their workload. With few exceptions, they decide which cases they hear and how many. Since the 1980s, the court’s docket has shrunk from approximately 150 each term to the current 70-80 with no explanation.

Individual justices also decide whether to withdraw from a case because of a conflict of interest or other reason. A justice’s refusal to withdraw can’t be appealed, and justices almost never explain why — or even why they don’t explain.

Accidents of history have long concentrated Supreme Court’s power even more — often in just one justice. During the past 40 years, the conservative justices have usually had a narrow 5-4 majority on most controversial issues, but usually one particular conservative justice has occasionally voted with the liberals.

In recent years, that justice has been Anthony M. Kennedy. In 2006-7, for example there were 25 5-4 decisions, about a third of the caseload, and Kennedy was on the winning side in all of them, giving the liberals seven victories. In 2010-11, Kennedy was on the winning side in 14 out of the 16 close cases, including Citizens United v. FEC, in which he wrote for the five-member majority. “It’s Justice Kennedy’s country,” Harvard law professor Noah Feldman said. “We just live in it.”

Yet justices are not accountable for their decisions to either the political branches or the electorate. Though Congress can theoretically overturn the court’s nonconstitutional decisions, it rarely does.

Such great, unaccountable power is anomalous in a democracy, but it is the price we pay for judicial independence. Independence does not, however, require that those who exercise such power do so until they die or choose to retire, which can be 30 to 40 years.

No other democracy in the world allows its judges such longevity. All mandate retirement at age 65 or 75, or a specific term of years. Every state but Rhode Island has also done so.

The price of life tenure is high. The last 10 justices to leave the court, either by death or by retirement, served an average of 26.4 years. Three served more than 30 years; four served 23 or more years, and one, David Souter, 19. Only Lewis Powell served a typical judicial term — 15 years.

By contrast, from 1789 to 1970, justices served an average of 15 years and retired at 68. The 10 most recent justices to leave court averaged 80.6 years. Six were 80 and older, Chief Justice Warren Burger was 79 and Sandra Day O’Connor and Byron White were 76. Only Souter left at a standard retirement age, 70.

No one, particularly not an unaccountable public servant in a democracy, should have such great power for so long. The Framers could not have foreseen that this would happen. Life expectancy in 1787 was far shorter and the job, which involved “riding circuit” on terrible roads over long distances, was not easy. The first 10 justices, for example, served an average of less than eight years.

The results of recent longevity have not been good. Power breeds arrogance — and Supreme Court justices are not immune.

Consider: The justices have refused to subject themselves to the Judicial Code of Conduct that governs the behavior of all other judges. One basic tenet of the code, and a fundamental principle of judicial ethics everywhere, is that judges do not attend politically partisan events — especially fundraisers. Nonetheless, Justice Samuel Alito, for example, has frequently attended an annual dinner that raises hundreds of thousands of dollars for the right-wing American Spectator and served as the event’s keynote speaker in 2008.

Some justices have also been intolerant of disagreement. The most notorious example is Justice Antonin Scalia, who regularly excoriates justices who differ with him.

Mental rigidity may accompany old age — which can make older people reluctant to understand the fast-moving technological, social and economic changes of the past 50 years. Mental capacities may also wane.

The legal historian David Garrow has chronicled 18 instances of serious mental decline among sitting Supreme Court justices — including major figures like Oliver Wendell Holmes, Thurgood Marshall and Powell. William O. Douglas and Stephen Field both had to be persuaded to resign by their colleagues.

Life tenure can also produce an uneven allocation of appointments among presidents. It enables the justices to try to influence the appointment of like-minded successors by strategically timing resignations, which is now a common occurrence.

When illness or death forces a departure, mere chance prevails. As a result, William Howard Taft had six appointments in his single presidential term, but Bill Clinton had only two during his eight years.

Many law professors, members of Congress, leading lawyers and even some Supreme Court justices have long called for an end to what University of Texas law professor Lucas Powe has called “the Framers’ greatest lasting mistake.” Many proposals set retirement at 70 or 75. But that won’t necessarily reduce lengthy tenures, because justices can be appointed in their 40s and early 50s.

The strongest suggestion is a single, nonrenewable term of approximately 15 years, a practice that many other courts with constitutional jurisdiction follow. The openings could be set at staggered intervals.

Judicial independence is essential to a democracy, but life tenure is not. It is time we corrected the Framers’ mistake.

Herman Schwartz is a constitutional law professor at the American University Washington College of Law.