|Rahm Emanuel stepped down from his role as chief of staff to pursue a possible bid for mayor of Chicago [EPA]
Rahm Emanuel, the White House chief of staff, is set to step down to pursue a possible bid to become mayor of the US city of Chicago.
Emanuel, a former member of congress and adviser for the Clinton administration before accepting the chief of staff position in November 2008, is expected to announce his resignation on Friday.
The White House would not confirm reports on the timing of the key aide's departure but said Barack Obama, the US president, had scheduled a personnel announcement for later in the day.
His departure will prompt Obama to appoint an interim chief of staff, with observers saying it looks set to be Peter Rouse, who is currently a senior adviser to the administration.
Emanuel has been intimately involved in every aspect of Obama's government, from Afghanistan to healthcare reform.
"There is not an important thing that has happened in this administration that we've been able to accomplish for the American people that has not involved heavily his signature," Robert Gibbs, the White House spokesman, said.
"The title 'chief of staff' in many ways, says it all. He has been the energetic, inspirational leader of us, taking the president's promises and agenda and enacting them into law."
Although staff shake-ups are common in the White House, Emanuel's departure is just the latest in a growing list of senior staff resigning their posts.
Members of the president's economic team have either gone or are on their way out and Robert Gates, the defence secretary, has signalled he will leave next year.
Darrell West, the vice-president of governance studies at the Brookings Institute, told Reuters news agency the roles are very demanding and that presidents often lose key staff at the two-year point.
"The fact the Democrats are expected to lose big in the November election is likely going to accelerate this staff exodus," he said.
"We are probably going to see additional people leave after the November election."
Emanuel started his political career as a policy adviser and fundraiser on Chicago mayor Richard Daley's 1989 campaign.
The chief of staff's plans have been the source of widespread speculation in both Chicago and Washington since Daley announced this month that he would not seek another term in the February election.
In a television interview in April, Emanuel had called it "no secret" that he would like to run for mayor.
Known as 'Rahmbo' by his friends and enemies, Mr Emanuel is notoriously tough and short-tempered, his conversations often laced with expletives.
James Hohmann, the national political reporter for the Politico website, told Al Jazeera that Obama had faced criticism for choosing him.
"Many have the view that Obama appointing Emanuel was aimed at pleasing Washington insiders, and not aimed at choosing a chief of staff that could connect with the American people," he said.
In 2005, the then-senator Obama joked about his future chief of staff's profane persona.
"He was working at a deli, an accident with a meat-slicing machine. He lost part of his middle finger. As a result of this, this rendered him practically mute," he said.