How long do Supreme Court justices serve?

Why this is the answer

Supreme Court justices serve for life. The official list accepts three ways of saying so: for life, lifetime appointment, or until retirement. The words in parentheses on the list are optional, so "life" or "retirement" on its own is fine. The rule comes from Article III, Section 1, which says that federal judges "shall hold their Offices during good Behaviour." There is no fixed term and no reelection. A justice keeps the seat until leaving it, and the official list names retirement as that point. The same section adds a guarantee about pay: a judge's compensation cannot be reduced while the judge stays in office. Alexander Hamilton defended the arrangement in Federalist No. 78. He called the good-behavior standard "one of the most valuable of the modern improvements in the practice of government." Under a monarchy, he wrote, it is a barrier against the ruler's despotism; in a republic, it guards against overreach by the legislature; and in any government it is the best way to secure a steady, upright and impartial administration of the laws. Because the seat lasts so long, the way a person gets it carries extra weight. Federal judges are not elected. The President nominates them, and the Senate must approve each one before that person can take the bench. The numbers that compete with "life" in an applicant's memory are the terms of elected officials. The President, for instance, is elected for four years and can be elected only twice. Those numbers have nothing to do with how long a justice serves. "Until the next presidential election" is also wrong, because a new President does not replace the justices already on the Court. The President has to go back to the voters, while a justice, once confirmed, never does.