It is merely a theory that explains how free enterprise works. Banks for example, a very important part of the economy, are left out. Some socities do not accept the circular flow model theory. These socities, therefore, choose another economic system other than capitalism. Socialists and communists see the role of the government in a different light than capitalists do.
The United States Constitution states that the Vice President of the United States is the President of the Senate, despite not being a senator, and that the Senate must choose a president pro tempore.
The Department is headed by the United States Attorney General, who is nominated by the President and confirmed by the Senate and is a member of the Cabinet. The current Attorney General is Jeff Sessions.