One of the common misconceptions about the US Supreme Court is that its appointments are for life.

The US Constitution simply states that justices "shall hold their Offices during good Behaviour." In recent decades, that clause has been interpreted, often with political motivations, in a broader manner.

The clause was designed to give justices long-term job security that would insulate them from the political pressures felt by presidents and legislators. But open-ended Supreme Court terms have only politicized the office more, critics say. With the prospect that a justice could serve – and vote a certain way – for 30 years or more, when a seat does open up the political stakes are that much higher. There's also the question about whether, in some cases, decisionmaking could be impaired due to age-related illnesses.

"We seem to have this tradition more and more of justices trying to stay absolutely as long as they can on the court," says Timothy O'Neill, a professor at the John Marshall Law School in Chicago.

With the sudden death of Justice Antonin Scalia last weekend, the debate over whether lifetime appointments best serve either the country or the bench has ramped up further. Not only could President Obama appoint someone who could conceivably serve into the 2050s, but he could shift the ideological balance of power in the court to the left for the first time since 1991 (and during a contentious election year, no less). He is now sparring with the Senate in what could become the longest Supreme Court nomination process in history. (The record for the longest wait between a nomination being received and a vote is 125 days for Louis Brandeis in 1916, NPR reports.)

"Presidents want to keep a legacy going for 40 years, so they want to appoint a younger person," Professor O'Neill says. "On the other side, they're thinking: 'We can't approve this person, they're going to be here for 40 years.' "

Advocates of term limits or mandatory retirement ages for the justices say such measures could reduce the politicization of the bench, by lowering the stakes. But, legal experts note, such measures come with their own challenges, including the possibility of justices "gaming the system" by putting off pivotal cases until the vote swings their ideological way.

Part of the reason for justices' lengthening tenures is because people are simply living longer, O'Neill says.

The average life expectancy at birth has increased from 47.3 years in 1900 to 78.7 years in 2010, according to the US Centers for Disease Control and Prevention, and that trend is reflected in the length of tenures on the Supreme Court.

Before 1900, only 26 justices served 10 years or more; since 1900, there have been 48 justices who have held their seat longer than 10 years, according to Slate. The last five justices were appointed while in their 50s, and legal experts say there’s a good chance one of them could be the first justice to serve more than 40 years (the current record belongs to William Douglas, who served for 36 years).

Longer lifespans have in turn bred a trend where presidents appoint younger justices, with a view toward preserving their ideology on the high court long after they've left office, legal experts say.

The justices themselves aren't above these political battles, either. The growth of a supporting staff of law clerks has meant justices can handle the workload at more advanced ages, experts say, allowing them to retire at a politically ideal moment. David Souter, who retired at age 69, and John Paul Stevens, who retired at 90, both factored the ideology of the sitting president in their decisions to retire, according to reports. (Justice Stevens told ABC News in 2014 that "it's an appropriate thing to think about your successor, not only in this job.")

The result of this, says David Garrow, a professor at University of Pittsburgh School of Law, has sometimes been justices continuing to serve after they no longer possess the mental ability to do so effectively. In his 2000 paper "Mental Decrepitude on the US Supreme Court," he recounts some of the more notorious anecdotes.

Justice Douglas finished his 36-year term dozing off during oral arguments. Joseph McKenna wrote an opinion "deciding the case one way when there had been a unanimous vote the other, including his own," according to colleague William Howard Taft. Frank Murphy was hospitalized more than once in the late 1940s, leading to his colleagues and a clerk authoring an opinion in his name. On the more extreme end, in the 1986 case Bowers v. Hardwick – which upheld Georgia’s sodomy law – an incapacitated Lewis Powell cast the deciding vote.

"The Court's problem is not length of service, but the extent to which the bench is dominated by justices who are past the age of 65 and whose powers inescapably weaken," writes Dr. Garrow in an e-mail to the Monitor. He would support a mandatory retirement age of 70 or 75.

Orin Kerr, a professor at George Washington University Law School, argues that an 18-year term limit would be a solution. In an op-ed this week for The Washington Post, he wrote that such a term limit would mean predictable vacancies every two years, leveling the political playing field somewhat.

Justices from previous times would cycle off the Court at predictable times, and they would be replaced by new Justices reflecting the current president and Senate. The ideological makeup of the Supreme Court as a whole would tend to reflect the president and the Senate at two-year intervals going back over the previous 18 years."

The American public seems to support this idea too. In the aftermath of major court rulings on the Affordable Care Act and same-sex marriage last year, a Reuters/Ipsos poll found that 66 percent of respondents – across party lines – favored a 10-year term limit. That also might lead to a court more in step with the mores of the times, supporters say.

But mandatory retirement ages or term limits present their own problems, O'Neill argues. It could lead to justices "gaming the system," he says, rejecting or deferring certain cases based on the knowledge that a justice, who may cast a deciding vote they disagree with, will soon be leaving. Senate rules might also have to change. If a president has to make two Supreme Court appointments each term, would the Senate then have to confirm them?

"I like the concept. It’s the implementation that I think we need to think about," he adds. "The more you think about this, the more issues you can come up with."

Another potential obstacle would be whether such a change would require amending the Constitution – something that would need to be ratified by both houses of Congress and three-quarters of the states.

"The change would be hard to make," wrote Professor Kerr in the Post. "But I think the effort would be worth it."

Paul Carrington – a professor emeritus of law at Duke University and author of the 2006 book "Reforming the Supreme Court: Term Limits for Justices" – is more optimistic about whether a retirement age or term limit could be implemented.

"I'm not sure there’s a constitutional impediment to that," he says. "The Constitution just says for 'good Behaviour,' and what is good behavior can be defined."

He points out the many state courts have mandatory retirement ages for judges – 32 states, according to the National Center for State Courts – and says Congress could simply pass a similar law for the federal court system.

It's harder to know how the justices themselves feel about the issue, but there are some clues.

In 1983, before he joined the court, current Chief Justice John Roberts suggested setting a term limit of 15 years to "ensure that federal judges would not lose all touch with reality through decades of ivory tower existence," according to a New York Times story from the year he was appointed. "It would also provide a more regular and greater degree of turnover among the judges," he said.

For her part, Justice Ruth Bader Ginsburg spoke about her reluctance to resign during Mr. Obama's term, as some had urged her to do in 2014, citing the Senate as a barrier. "If I resign anytime this year, he could not successfully appoint anyone I would like to see in the court," she said in a 2014 interview with Elle. "As long as I can do the job full steam ... I think I'll recognize when the time comes that I can't any longer. But now I can."

Justice Scalia also spoke in interviews about continuing until he no longer enjoyed or felt up to the work. But in a 2013 interview with New York magazine's Jennifer Senior, he expressed some concerns: "You always wonder whether you’re losing your grip and whether your current opinions are not as good as your old ones."