That wasn’t the reality in the early decades of the Supreme Court. More than 80 percent of those confirmed in the early 1800s died during their tenures. By contrast, only 11 percent of those confirmed in the second half of the 20th century died in office; the rest retired. Modern justices are more likely to survive serious illnesses. Justice Ruth Bader Ginsburg, 85, for example, has survived both colon and pancreatic cancer (and recently said that “I have about at least five more years” on the Court). Justice Sonia Sotomayor, 64, has had Type-1 diabetes since childhood.

Supreme Court nominations have become increasingly rare. One recent analysis estimated that only 25 justices will be appointed in the coming 100 years, compared with 47 appointed in the last 100 years. That means the consequences of each nomination are growing larger and the political battles more heated. A justice experiencing mental decline may be more likely to stay on and retire during a presidential term in which a successor could carry on his or her legacy.

As judges routinely serve into their 70s and 80s and beyond, some courts — but not the Supreme Court — are taking significant steps to make sure judges are mentally sharp. The 9th Circuit Court of Appeals, for example, holds regular seminars to teach judges about signs of mental decline. It also encourages judges to have cognitive tests and designate colleagues or loved ones who can intervene if necessary.

The United States is rare among democracies in guaranteeing life tenure to judges on its high court. Most U.S. states have term or age limits for its judges — generally between 70 and 75. Vermont is an outlier with an age limit of 90. Recent polling shows that a majority of voters in both political parties support term limits for Supreme Court justices.

Of course, with modern medicine and longer life spans, Supreme Court justices can continue gaining experience and wisdom — in other words, they can keep getting better at their jobs. But in a polarized era, youth has become a priority along with judicial experience and quality in selecting a nominee.