The chief justice of the United States is the chief judge of the Supreme Court of the United States and the highest-ranking officer of the U.S. federal judiciary. Article II, Section 2, Clause 2 of the U.S. Constitution grants plenary power to the president of the United States to nominate, and with the advice and consent of the United States Senate, appoint "Judges of the supreme Court", who serve until they resign, retire, are impeached and convicted, or die. The existence of a chief justice is explicit in Article One, Section 3, Clause 6 which states that the chief justice shall preside on the impeachment trial of the president. The chief justice has significant influence in the selection of cases for review, presides when oral arguments are held, and leads the discussion of cases among the justices. Additionally, when the court renders an opinion, the chief justice, if in the majority, chooses who writes the court's opinion; however, when deciding a case, the chief justice's vote counts no more than that of any other justice. Article I, Section 3, Clause 6 designates the chief justice to preside during presidential impeachment trials in the Senate; this has occurred three times. While nowhere mandated, the presidential oath of office is by tradition typically administered by the chief justice. The chief justice serves as a spokesperson for the federal government's judicial branch and acts as a chief administrative officer for the federal courts. The chief justice presides over the Judicial Conference and, in that capacity, appoints the director and deputy director of the Administrative Office. The chief justice is an ex officio member of the Board of Regents of the Smithsonian Institution and, by custom, is elected chancellor of the board. Since the Supreme Court was established in 1789, 17 people have served as Chief Justice, beginning with John Jay (1789–1795). The current chief justice is John Roberts (since 2005). Five of the 17 chief justices—John Rutledge, Edward Douglass White, Charles Evans Hughes, Harlan Fiske Stone, and William Rehnquist—served as associate justices prior to becoming Chief Justice. Origin, title and appointment The United States Constitution does not explicitly establish an office of Chief Justice but presupposes its existence with a single reference in Article I, Section 3, Clause 6: "When the President of the United States is tried, the Chief Justice shall preside." Nothing more is said in the Constitution regarding the office.