The person of President is one-third of the US government -- the executive branch. All the cabinet and executive branch departments are extensions of the Presidential office. Most are manned by civil service personnel, who may or may not agree with the President. But, they wren't elected, he was. To ensure the President's agenda is carried out, he has a number of political appointments (about 900) from Cabinet level down he is, allowed by law to appoint. Some with the approval of the Senate, some not.
I am quite aware of the use of political officers in old Soviet Union, and the president's appointees aren't the same. No one elected the Politburo or the appartchik.