The independence of the judicial branch is ensured by making sure that the judges cannot receive a reduction in their salary and cannot be removed from the bench by a president who might oppose the judge's views. This gives judges a security in their job that allows them to make decisions without worrying about political pressures.
The United States Constitution created these two protections in order to ensure that the judicial branch's decisions would remain independent. The Constitution is full of checks and balances between the three governmental branches in order to keep the country running smoothly. Judges for the Supreme Court are appointed by the president with advisement from the Senate.
President William Howard Taft was one of the leaders in the development of institutions of a judiciary nature that could govern themselves. For many years, judiciary courts still needed administrative support from the government's executive branch. Taft felt that this created too much of an interdependence between the two and sought to eliminate this interdependence in many ways.
There have been court critics through the years that are unhappy with judicial independence; however, as Taft was able to recognize, the constitutional protection of judges depends on public faith as well as a responsive court system. The public faith only exists when the public believes that political parties will be unable to influence the judicial process, which requires an independent judicial system.