That White House chief of staff Rahm Emanuel will announce shortly whether he intends to leave to run for mayor of Chicago is not news. Smartly, the White House, knowing that Emanuel was planning to leave the White House after two years in any event, is using Daley's retirement to frame the eventual notice from Emanuel that, after the midterms, he will step down. This helps to avoid the "Rats Fleeing From A Sinking Ship" news coverage that will be occasioned by the departure of other senior administration officials after the midterm.

But the departure of the chief of staff is a singular event, because the position is so unique in the world. In the U.S., where political appointees number in the thousands, the chief of staff is their de jure boss. (One reason why the U.K. has never formalized the role is that there are so few political appointees.)  But Emanuel is also the man on the hook for the millions of career employees, members of the military and the civil service. His role and its power are too broad to define. An entire sub-field in political science has been created to study the position itself. Most academic courses on the White House spend ample time on the chief of staff. 

Some of the chief's informal powers are more significant than his titular powers.

Briefly, a chief of staff is a gatekeeper -- he sets the rules of access to the Oval Office and the President. He manages the top of the pyramidal interagency policy process that sifts through what information the President gets and what information he does not get.  A chief of staff is a secret keeper. There is not a single classified thing the President learns that his chief also does not learn. Believe it or not, there are things that President Obama knows that his National Security Adviser does not. But Rahm does. He manages the relationship with the cabinet. Some chiefs of staff facilitate a form of strong cabinet government, while others spend time trying to corral the cabinet. (Rahm chose the latter course.)  He sets the tone for the White House: calm versus frenetic. Fun or sober. (Rahm's White House is frenetic and fun.) He sets and manages the relationship with senior members of other political institutions: the House, the Senate, the Pentagon, business, liberal groups, the media. He manages the rivalries among the factions and power centers that surround the president himself. He must not get in the way of the president's other important relationships, either.

A good chief of staff must be able to do all of the above, and do it with the blessing and confidence of the President. To the dismay of some of Emanuel's critics, President Obama has -- and has had -- complete confidence in Emanuel to be his prime minister. That does not mean that Obama wants an Emanuel clone in the job over the next two years, which will require a different set of skills.

Primarily, the next chief of staff must:

Get things accomplished with a diminished majority without losing sight of Obama's vision. No school uniform stuff. No midnight basketball. 

Keep a tired and probably demoralized WH staff and Cabinet motivated. This is going to be a tough stretch.

Have enough political savvy to essentially co-manage a presidential campaign.

Have the self-discipline not to give into 24-hour cable commentator babble; have a long-term outlook and be able to design and executive long-term messaging plans.

Have the self-confidence to work side by side with Valerie Jarrett, the president's closest aide, and to not be bothered by her personal relationship with the President. The chief needs to set up a counter-structure to prevent the president from cocooning into his Chicago shell.