More senior White House staff are to leave in the next few months, adding to the high exit rate from President Obama's administration.
Political analysts attribute the attrition rate to exhaustion, but Republican opponents blame disarray inside the White House.
The imminent departures include those of defence secretary Robert Gates, who has said he hopes to retire early next year, and Obama's senior White House adviser, David Axelrod, who is planning a return to his home town of Chicago early next year to concentrate on planning for Obama's 2012 re-election bid.
The White House press secretary, Robert Gibbs, has been mentioned in the past few weeks in connection with a range of jobs, including White House adviser or chairman of the Democratic national committee, which runs the party.
This follows the departure of the national security adviser, General James Jones, after less than two years in office, as well as almost the entire economics team, of whom Peter Orszag and Christina Romer have already gone.
Larry Summers is due to return to Harvard before the end of the year. The chief of staff, Rahm Emanuel, left last month to stand for mayor of Chicago.
The changes provide Obama with a chance to reshape his team after the November 2 midterm elections, in which polls indicate the Republicans stand to make big gains.
Obama's popularity in opinion polls has dropped from 70% last year to the mid-40s this year, so a reshuffle offers an opportunity to reverse that trend and to change economic and foreign policies and political strategy.
In a blog on the Politico website, Alvin Felzenberg, the presidential historian writes: "These departures are a reflection of Obama's leadership style. Why he has such a difficult time earning and retaining the loyalties of people outside his circle of intimates is anyone's guess."
Gibbs last month attributed the changes to 15-or 16-hour work days, seven days a week.
"These are worn-out, depleted people who are not waiting for the fire alarm to be sounded before heading for the emergency exit,"said Professor Ross Baker, a political scientist.