United States Defence Secretary Chuck Hagel's sudden resignation has sparked a storm of speculation in the US capital, with many wondering why the Pentagon chief is leaving the post at a time when the US military is engaged in major challenges abroad.
Theories range from a need to bring in someone better equipped to handle the conflict in the Middle East, to Mr Hagel serving as a political scapegoat for the US' faltering policy in the Middle East and eastern Europe.
A persistent rumour has been that Mr Hagel irked the White House over criticism of the strategy in the fight against the Islamic State in Iraq and Syria (ISIS). President Barack Obama has insisted that there be "no boots on the ground" while Mr Hagel is said to favour a more forceful approach.
There is also the suggestion that Mr Hagel was out of his depth in dealing with the conflict, having been appointed primarily to lead the Pentagon through budget cuts.
Whatever the reason, nearly all Washington pundits agree that Mr Hagel's resignation was not the "mutual decision" the administration stressed it was.
Mr Hagel, 68, was noted for being strongly committed to Mr Obama's push for stronger engagement with Asia, visiting the region four times in the past year.
He is a Vietnam War veteran with two Purple Heart medals.
Under Mr Hagel, the US has taken a tough line in the territorial dispute between China and Japan that covers a large area of air space and several small islands in the East China Sea.
Late last year, China declared an air defence identification zone in the area. Within days, the US flew two long-range B-52 bombers through the zone in a clear message to China.
The official announcement of Mr Hagel's resignation was made in the state dining room of the White House on Monday. There was no sign of any animosity between the defence secretary, President Obama and Vice-President Joe Biden. Mr Obama hugged Mr Hagel and paid tribute to him as a "great friend".
"Last month, Chuck came to me to discuss the final quarter of my presidency and determined that, having guided the department through this transition, it was an appropriate time for him to complete his service," said Mr Obama.
Mr Hagel said his term as Pentagon chief was the "greatest privilege of his life".
Within hours of the announcement, several names emerged as likely successors. At the top of the list is former under-secretary of defence for policy Michele Flournoy.
If appointed, she would be the first woman to take up the post.
Other contenders include two deputy secretaries who served under Mr Hagel, Mr Ashton Carter and Mr Robert Work.
In an editorial, The New York Times said Mr Hagel was not a strong defence secretary but also that he was not the core of the Obama administration's military problem.
"That lies with the President and a national security policy that has too often been incoherent and shifting at a time of mounting international challenges, especially in Iraq, Syria and Afghanistan," the paper said.
While the White House pledged to pick a new defence secretary quickly, the confirmation - which would take place under the new Republican-controlled Senate - could take months to complete.
This article was first published on Nov 26, 2014.
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