By Jill McGivering
BBC State Department correspondent
In many ways, Colin Powell will be a tough act to follow.
Powell said it had been a great honour to serve his country
Throughout the first term, he was consistently one of the most popular members of the Bush cabinet, with enviably high ratings on personality and integrity.
When State Department spokesman Richard Boucher agreed on Monday that there might be some lower level departures at the State Department now too, he explained it by saying there was something about working with Secretary Powell that made many people stay in their jobs longer than they might have otherwise.
The candidates being discussed so far don't have that Powell common-touch charisma.
For months, the talk at the state department has been that if Mr Powell were to leave, his most likely successor might be Condoleezza Rice, the current national security advisor.
Some claim the job is hers for the taking. The only reason she might turn it down, some speculate, is because she really wants the defence portfolio. But so far, Donald Rumsfeld is still in place and there is little sign of his post becoming vacant.
'Innermost circle' member
In some ways Ms Rice is an obvious choice.
Rice is a close friend as well as political ally of Bush
President Bush is said to prefer to promote from inside, choosing figures who are tried and tested and already high profile, especially for such an important post.
Ms Rice is described by some as so close to the president that she's almost family. As well as being in the innermost circle, she's of the same mind as the president on many policy matters.
The Bush administration seems keen to exert firm control over the state department, not choose another secretary who might have different views.
Ms Rice's appointment would certainly bring the state department strongly back into the fold.
Place in history
She is also seen as highly ambitious, keen to make her mark.
As the first black female secretary of state, she would win a place in the history books.
Much of the foreign policy focus in the second term is likely to be firmly on the Middle East - but Ms Rice's background as a Russian expert would also prove useful at a time of concern about President Vladimir Putin's handling of political and civil rights.
Observers have said her main rival for the post was US Ambassador to the United Nations John Danforth.
As well as being a former Senator, he is a paternal figure, experienced, diplomatic and, as an ordained minister, seen as having high personal integrity and moral values.
Before he served at the UN, President Bush chose him as his special envoy to Sudan, tasked with negotiating peace in the north-south civil war.
In some ways, he would be a comforting appointment, a trusted figure who would be accepted across the political divide.
A more cynical view is that he would also be seen as compliant - an implementer of policy rather than someone likely to prove a thorn in the administration's side.