Final answer:
Positions in direct support of the President of the United States are known as White House Staff. These include various advisers and assistants, such as the White House Chief of Staff, and most do not require Senate confirmation. The role and number of White House Staff have grown significantly over time.
Step-by-step explanation:
Positions to which individuals are assigned duties on a permanent or full-time basis in direct support of the President of the United States are known as White House Staff. The Executive Office of the President (EOP), which includes the White House Office (WHO), contains the president's personal staff of assistants and advisors. Most of these positions are not subject to Senate confirmation and are appointed at the president's discretion. The White House Staff makes many decisions, acting in the name of the president, and this staff can be quite large, including a variety of roles such as political advisers, speechwriters, the press secretary, and others.
While the president also appoints individuals to federal departments or agencies, many of which are listed in the "Plum Book" and require Senate confirmation, the White House Staff operates more closely with the president on a day-to-day basis. The size and composition of the White House Staff has grown substantially since Abraham Lincoln's time and involves more than 450 individuals directly within the White House, with additional staff in the broader EOP.