The council is no place for political creatures, many have argued. It is the place where the nation’s deepest intelligence secrets, its fluctuating hierarchy of national interests and its jockeying-for-power cabinet members combine as policy differences are hashed out. It is the forum where decisions about war, from Vietnam to Iraq; drone strikes in Pakistan; and conflicts in cyberspace have unfolded over endless hours of meetings.

Of course, with stakes that large, it has always been about politics — from grand strategy to petty scorekeeping. Here is a quick look.

So what is the National Security Council, and why does it exist?

The nation lived without the council for more than 150 years, until World War II ended and the immense responsibilities of managing the world — and the atomic bomb — descended on President Harry S. Truman. The council was created in 1947, when the C.I.A. and the Defense Department came into being. Like most things in Washington, it started small and, over time, ballooned to such size that every new president swears the first thing he will do is pare it back.

Which, of course, never really happens.

Why is it viewed as so powerful?

Presidents of both parties have one thing in common: They are control freaks. And the council becomes the instrument of control. “Each individual president has tremendous latitude to shape both the institution of the N.S.C. and the formal and informal mechanisms of his or her White House national security apparatus,” David Rothkopf wrote in his history of the council, “Running the World.”

The council is “all about the influence of one person,” Mr. Rothkopf wrote.

The formal instrument is the “principals committee,” made up of the president, the vice president and all those jockeying cabinet members. That is what Mr. Bannon joins, meaning he won the first week’s access-trust-influence sweepstakes. The chairman of the Joint Chiefs of Staff and the director of national intelligence, who were regular members of the council under President Barack Obama, would attend if “issues pertaining to their responsibilities and expertise are to be discussed.”