The principle of the separation of powers in government was enacted by the drafters of the United States Constitution in order to guard against the possibility of a single individual or group seizing tyrannical powers. This goal was implemented through the separation of branches of the Government between the executive, legislature, and judiciary. In this system, the Supreme Court functions as the highest authority of the judicial branch, as well as one which, to some extent in Constitutional theory and to an increasing degree in practice, exercises some authority over the other branches. This authority has been used to enact an array of sweeping changes in American law, despite the more limited role of the Supreme Court in comparison to the other branches, which largely consists of appellate oversight over lower court decisions.
In order to allow for the principle of the separation of powers to assure the effectiveness of the Supreme Court, the Constitution contains stipulations by which the Court is implicitly separated from the other branches. Maintaining a separation of branches in this way is intended to secure the Supreme Court the ability to effectively exercise the power which it is given under the Constitution without interfering with the other functions of Government.
One of the important ways in which the separation of branches is enacted in regard to the Supreme Court is through the principle of lifetime appointment. As with much else in the Constitution, this move toward the separation of powers is not clearly stated as such, but has been interpreted from the Constitutional stipulation that Justices be allowed to "hold their Offices during good Behavior". In practice, this rule has been taken to mean that Justices cannot be removed from the bench unless they are proved, such as by Congressional impeachment, to be unfit for holding the office.
An early and prominent example of this rule is furnished by the career of the fourth Chief Justice, John Marshall, who served for 34 years from his appointment in 1801 to his death in 1835. During his term Marshall demonstrated the strong role which could be taken by a Justice through the separation of branches.
A supporting provision to the principle of lifetime appointment is that sitting members shall "receive for their Services a Compensation which shall not be abridged" at any point during their term. Through these rules, the separation of powers is enforced for the judicial branch by providing against procedural attempts by the legislature or executive to influence or intimidate the judiciary's members.
The separation of powers in regard to the Supreme Court is also enacted to the executive and legislature's benefit by their powers of appointment toward the membership of the Supreme Court. To some extent, however, this practice also provides for an implicit separation of branches setting the judiciary apart from the legislature and executive. While those sections of Government are subject to the decisions of the electorate, the Supreme Court is implicitly set apart in being filled solely through appointment.