The part of the Constitution that mentions life tenure for federal judges is Article I, Section III, which states that “judges, both of the supreme and inferior courts, shall hold their offices during good behavior.”
But the term “offices” has never been defined by Congress, unlike, say the number of “inferior courts” or how much federal judges should be paid.
Congress could end life tenure for Supreme Court justices by defining the term “office” as the office of federal judge, which would still be held for life, but then would specify that only 18 years of one’s judicial service may occur on the high court.
That means an individual serving on the Supreme Court for 18 years would then have the opportunity to serve on a lower federal court for as long as he or she wishes, as retired Supreme Court Justices Sandra Day O’Connor and David Souter are doing this very day.
And this process of ensuring individuals aren’t serving on the high court for 30 or 35 years*, which has recently become customary, could take place without the arduous task of amending the Constitution.
For reasons why ending life tenure is a good idea for our democracy, visit this page.
*Such a law would be prospective and would not limit current justices’ service to 18 years.