There are always power centers in any White House. Certain people have their own little fiefdoms or specific knowledge of how government bureaucracy works, which gives them a leg up in internecine battles. Some offices or Cabinet posts are just imbued with more power than others. The Treasury secretary, for example, is always going to have more juice than the secretary of agriculture, just by virtue of their respective portfolios. But there is no job that has traditionally been more powerful than White House chief of staff.
The role of the position is multi-faceted, managing the flow of information to the Oval Office and keeping them from becoming distracted by people pushing their own agendas and distorting the president’s understanding of the facts. The chief of staff has hiring and firing power over the West Wing, basically running the day-to-day operation of the presidency. Mediating disputes among the executive branch’s advisers and officials before they reach the president is also an important part of the job. But most importantly, the chief of staff should be the president’s most trusted adviser, willing to provide an honest assessment and opinion on all the important issues that reach the Resolute Desk.
