The likely departure of the White House Chief of Staff, Rahm Emanuel, to run for Mayor of Chicago is part of a half-term reshuffle of top aides that will signal a new chapter in the history of Barack Obama's increasingly embattled presidency.
It also raises a vital question: will Mr Obama continue to rely on the small and trusted group of intimates who have followed him from Chicago to Washington – or will he seize the chance to bring in new blood from the outside to invigorate an administration high command that critics say has become insular and out of touch?
The official word at the White House remains that Mr Emanuel is still "in the process of thinking about what he's going to do next". Unofficially, it is virtually taken for granted he will leave. The filing deadline for the race to succeed the outgoing mayor, Richard Daley, is 22 November, and the Chicago Sun-Times reported yesterday that Terry Peterson, head of the city's transit authority, had signed up as Mr Emanuel's campaign manager.
Among the possible replacements as Chief of Staff (whose role is to take charge of the day-to-day running of the White House and advise the President) are Pete Rouse, a senior Obama adviser; Tim Kaine, the former governor of Virginia; and Tom Donilon, the deputy national security adviser to General James Jones. But Gen Jones, too, is said to want to leave by the end of the year.
Another impending departure is that of David Axelrod, a key adviser and architect of the 2008 campaign, who has been to President Obama something akin to what Karl Rove was to George W Bush. Mr Axelrod is also set to head to Chicago some time after the mid-term elections on 2 November, to plan President Obama's 2012 re-election bid. "I've been pretty clear ... that at some point, I'm going to go back and work on the re-election campaign," he said this week.
No less of an upheaval looms in the President's economic team. After two years as director of Mr Obama's National Economic Council, the abrasive Larry Summers is returning to his former professorship at Harvard, while Peter Orszag, the budget director, and Christina Romer, head of the Council of Economic Advisers, have already left. There are hiccups ahead in the wider government, too, with Defence Secretary Robert Gates signalling his intention to step down well before the President's term is complete.
Mr Obama is said to be keen for a woman to replace Mr Summers, and among the names mentioned are Anne Mulcahy, a former chairwoman of Xerox, and Laura D'Andrea Tyson, a top economic adviser at the Clinton White House.
However dramatic in appearance, such staff turnovers are anything but unusual at the White House, with its gruelling working hours, round-the-clock pressure and disruption of family life – not to mention all those large egos cooped up in a small space, and salaries that are often far below those in the private sector.
Andrew Card's stint of five and a half years under George Bush was very much the exception. Both Ronald Reagan and Bill Clinton got through four chiefs of staff in their eight years in office. George Bush Senior had three in his single four-year term.
Mr Emanuel, whose performance has won praise and blame in equal measure, made no secret of his ambivalence about taking the job when Mr Obama offered it days after his election victory in November 2008. Then a senior Democratic Congressman, he eventually accepted, but at the price of forfeiting a career on Capitol Hill that many believed would one day take him to the Speakership. More recently he has not concealed his interest in becoming mayor of his native Chicago, in the footsteps of the Daley dynasty.
The focus will now be on how Mr Obama remodels his team. Incoming presidents, from John F Kennedy and Jimmy Carter to Bill Clinton and George Bush, have relied, initially at least, on a small group of trusted advisers they have known for years. Mr Obama followed that pattern, with a "Chicago Mafia" consisting of people like Mr Axelrod, Valerie Jarrett and David Plouffe, his 2008 campaign manager.
But as the President's troubles have grown – his approval ratings have fallen from over 70 per cent in early 2009 to the mid-40s today, and his party faces heavy losses in November – so has criticism of the White House team among many Democrats.
Mr Obama himself is increasingly, if unfairly, described as over-analytical and short of empathy with ordinary Americans struggling to cope with the economic downturn. The looming staff shake-up may be his last opportunity to correct those impressions.
Exit Poll: The presidential aides on the way out
White House Chief of Staff
The President's chief enforcer has long hoped to be mayor of Chicago – and the timing might suit Obama, in particular if a chastening mid-term result dictates a more conciliatory approach to the Republicans.
After a lengthy period at the Pentagon, where he also served George W Bush, Gates has made it clear that he has no intention of seeing out Obama's first term. He is likely to delay his departure until 2011 given the other issues now on the President's plate.
Director of the National Economic Council
Although the announcement of his impending departure inevitably set tongues wagging, those closest to him insist it was because he did not want to lose his tenure at Harvard. Looming mid-terms may mean the President makes a consciously pro-business choice of replacement.
General James Jones
National Security Adviser
Once a key influence on the president's decision making on Afghanistan, he has since fallen out badly with Obama's closest advisers. Fallout from Bob Woodward's book detailing those relationships may only increase his rumoured anxiety to depart before the end of the year.
One of the most trusted aides from the campaign, Axelrod could depart the White House to begin work on a re-election bid. His departure as well as Emanuel's would transform the tight-knit cabal that surrounds Obama.