By Paul Reynolds
World affairs correspondent, BBC News website
The resignation of Colin Powell and the selection of Condoleezza Rice as secretary of state means that in President Bush's second term, the State Department should be firmly under White House influence.
Condoleezza Rice is a particularly close ally of the president
Condoleezza Rice is so closely allied to Mr Bush's interests that it is difficult to see how she would diverge, even if she comes under the influence of the State Department which tends to take a longer term view of world affairs.
Her promotion from her role as national security adviser is the latest swing of the pendulum in the delicate balance of power in Washington between the White House staff and the State Department.
Tension between the State Department and the National Security Council is part of the American way in foreign policy. Sometimes, in the White House view, the location of the State Department in the "Foggy Bottom" area of Washington also refers to the view of the world as seen by its rivals.
"The State Department and the White House tend to go in different ways," says John Dumbrell, professor of politics at Leicester University. "The problem is that the State Department is a separate bureaucracy, with closer contacts with Congress, and the White House staff serve the political needs of the president.
"The State Department has lost power over the past 30 years as influence has moved to the White House."
The source of this tension was a decision taken by President Truman in 1947 to set up the National Security Council. Truman brought several key members of his cabinet together under his chairmanship to discuss and decide foreign policy. His predecessor, President Roosevelt, took decisions by himself. A small staff served the council's interests.
In 1953, President Eisenhower made the head of that staff into a national security adviser. At first, this was a bureaucratic-type appointment, but in due course the post developed into a second senior voice in foreign affairs.
The national security adviser takes into account the range of opinion across government and presents his or her summary and recommendation to the president.
The State Department is an important voice, but only one voice. The Defense Department will have a view - so will the CIA and other departments. Differences are supposed to be hammered out in the National Security Council.
It doesn't always happen.
"In Washington," said Philip Davies, professor of American studies at de Montfort University, "personal relations often replace party loyalties and determine who has the final say.
"But there has been a long-term suspicion of the State Department since Senator Joseph McCarthy came up with his lists of mythical traitors there in the 1950s. Hardliners feel that secretaries of state tend to 'go native' more than the national security advisers."
The most notorious falling out between national security adviser and secretary of state came under President Nixon, when the powerful figure of Henry Kissinger was the adviser. It was really Kissinger who transformed the role into the powerful influence it is today.
He and President Nixon simply took the key decisions between themselves - over Nixon's visit to China in 1972 and the bombing of Cambodia during the Vietnam War, for example - and the poor old secretary of state, a lawyer named William Rodgers, was ignored.
Kissinger then solved the problem of clashes between the White House and the State Department by taking both jobs himself when Rodgers resigned.
It has become a sport in Washington to detect differences of view between the holders of the two posts.
There were clashes in the Carter administration between the mild and moderate Secretary of State Cyrus Vance and the more passionate National Security Adviser Zbigniew Bzrezinski.
Vance eventually resigned in 1980 over the failed raid to try to free the hostages at the American embassy in Tehran.
Winners and losers
It is not always the national security adviser who wins. Under Ronald Reagan in the 1980s, National Security Advisers Robert McFarlane and John Poindexter were implicated in the plot to sell weapons to Iran and use the money to support the Contra guerrillas in Nicaragua.
Secretary of State George Schultz was not directly involved, capitalised on their failings and went on to play a distinguished role in helping to bring the Cold War to a peaceful end.
The system is unlikely to be significantly changed. Presidents seem to like having more than one source of foreign policy advice. It gives them more power themselves to pick and choose. And they have the final say.