one-third of the justices have been U.S. military veterans. Samuel Alito is the only veteran currently serving on the court. Retired justices Stephen Breyer and Anthony Kennedy also served in the U.S. military. Retired justices There are currently four living retired justices of the Supreme Court of the United States: Sandra Day O'Connor, Anthony Kennedy, David Souter, and Stephen Breyer. As retired justices, they no longer participate in the work of the Supreme Court, but may be designated for temporary assignments to sit on lower federal courts, usually the United States Courts of Appeals. Such assignments are formally made by the chief justice, on request of the chief judge of the lower court and with the consent of the retired justice. In recent years, Justice Souter has frequently sat on the First Circuit, the court of which he was briefly a member before joining the Supreme Court; and Justice O'Connor often sat with several Courts of Appeal before withdrawing from public life in 2018. The status of a retired justice is analogous to that of a circuit or district court judge who has taken senior status, and eligibility of a Supreme Court justice to assume retired status (rather than simply resign from the bench) is governed by the same age and service criteria. In recent times, justices tend to strategically plan their decisions to leave the bench with personal, institutional, ideological, partisan and sometimes even political factors playing a role. The fear of mental decline and death often motivates justices to step down. The desire to maximize the court's strength and legitimacy through one retirement at a time, when the court is in recess and during non-presidential election years suggests a concern for institutional health. Finally, especially in recent decades, many justices have timed their departure to coincide with a philosophically compatible president holding office, to ensure that a like-minded successor would be appointed. Seniority and seating For the most part, the day-to-day activities of the justices are governed by rules of protocol based upon the seniority of justices. The chief justice always ranks first in the order of precedence—regardless of the length of their service. The associate justices are then ranked by the length of their service. The chief justice sits in the center on the bench, or at the head of the table during conferences. The other justices are seated in order of seniority. The senior-most associate justice