Within hours of US Secretary of Defense Chuck Hagel announcing his resignation, candidates to replace him were being named. Within a day, two out of the top three rumoured candidates removed themselves from contention. So the quest to find a new Secretary of Defense is becoming a case of 'who's left?' Given the challenges abroad, and more importantly at home, this is understandable.

Tom Switzer pointed briefly to the 'gruelling confirmation hearings' that await a Secretary of Defense nominee before the now Republican-controlled US Senate. The reputation for intense scrutiny experienced during these sessions has already forced high profile Obama Administration candidates to reconsider.

But to say the domestic concerns of a new Secretary of Defense end there would be incorrect. Consider for a moment the unenviable position of managing the world's most powerful military amid budgetary uncertainty and while conducting a military campaign in the Middle East.

But perhaps the greatest domestic challenge confronting a new Secretary of Defense is his or her place within the Obama Administration. The resignation of Chuck Hagel has led some informed commentators to believe he was a victim to what is seen as the White House's increasing centralisation of national security decision-making. Tom Ricks of Foreign Policy wrote:

Unless you have total White House backing in the first place, the job is almost impossible. Without such a commitment, it is just a nightmare.

Obama's eventual nominee will reflect a desire to either increase or decrease this trend of centralisation. Obama can pick a Secretary of Defense either because he/she will advocate and execute White House policy, or because he/she can be trusted to work in relative autonomy. These qualities are not mutually exclusive, but they won't always synchronize. The President's eventual choice will reflect his preferences and determine the direction of US National Security policy for the foreseeable future.

Photo courtesy of Flickr user US Department of Defense.