By Paul Reynolds
World affairs correspondent, BBC News website
Getting down to business: Mr Obama and Mr Biden meet the transition team
The announcement by President-elect Barack Obama's transitional team that once in office he will move quickly to countermand executive orders issued by President Bush is a signal that the change promised during the campaign is on the way.
It is certainly not unusual for a new president to change executive orders issued by the old. Indeed, it is quite normal.
But it is unusual for an announcement to be made so far in advance of inauguration (20 January, 2009) and to be so detailed.
In 2001, when George W Bush took office, his press spokesman Ari Fleischer said simply at the beginning of January that the outgoing President Bill Clinton had a been a "busy beaver" in issuing masses of executive orders and that these would be reviewed.
Now we are getting into the detail already. John Podesta, once Mr Clinton's chief of staff and currently head of Mr Obama's transitional team, has been on television to herald the changes. We know that the priorities will be to unblock research on stem cells, to stop drilling in certain environmentally sensitive areas within the US and to allow the state of California to tighten up regulations for vehicle emissions.
The early announcement by the Obama team might also be seen as a pre-emptive strike against the possibility that Mr Bush might himself order a flurry of changes before he leaves office, much as Mr Clinton (and Jimmy Carter before him) did. The warning is that anything Bush can do, Obama can undo.
An example of how an executive order can influence policy can be seen in the to-ing and fro-ing over abortion. President Ronald Reagan ordered that international aid groups that provided counselling on abortion should be denied US aid funds. Mr Clinton reversed the rule. Mr Bush changed it back and President-elect Obama is already under pressure to change it again.
Armoury of presidents
The executive order is part of the armoury of new presidents to impose change quickly and easily. They can act without having to get legislation passed by Congress.
For that reason, there is quite a bit of opposition to the increasingly widespread use of these orders, especially during periods when presidents do not command a majority in Congress, as happened under Presidents Clinton and Bush.
Paul Begala, an adviser to Mr Clinton, said once: "Stroke of the pen. Law of the land. Kinda cool."
Orders can be relatively modest - one of the first uses was by President George Washington when he announced Thanksgiving Day in 1789.
But they can be huge - as in the Emancipation Proclamation to free slaves by President Abraham Lincoln in 1862.
"We are talking about transition these days much more than we used to," said Esther Jubb, formerly of John Moores University in Liverpool, who has studied the process.
"Executive orders are a quick way for a president to legislate without having to go through Congress. As long as there is no budgetary requirement, a president can do things like changing or setting out rules for implementing policies. The orders are not mentioned in the US Constitution but they have grown up by precedent and as the president is in charge of implementing policies, he has wide scope for decisions."
At a time like now, when it is felt that a new era in US politics might be starting, President-elect Obama perhaps does not want the enthusiasm he encountered and encouraged to dissipate during the transition.
Barack Obama wants a sense of urgency and does not want to waste this period
"George Bush has looked increasingly irrelevant and Obama is forming a strong presidency-elect," said Professor Philip Davies of de Montfort University, also chairman of the British Association for American Studies.
"There is now a sense of the world and nation facing a crisis as in the 1930s, so Obama may be making an early statement to indicate that he will bring in change.
"In the 1930s President Roosevelt could pass legislation. He did so like nobody's business. But he, too, announced by executive order a six-day bank holiday to impose calm on the markets.
"Others have worked more slowly. President Nixon came to power in 1968 vaguely promising to do something about Vietnam and it was not until 1972 that he came out against the war more clearly and even then it took time to wind it down.
"Ronald Reagan on the other hand acted fast, but through Congress. He brought in an omnibus budget bill to change the budget in the current year. Normally presidents waited for the following year. But Reagan got one passed that gave effect to tax and spending cuts. It signalled that he was not the dumbo he was thought by some to be, but had a clear handle on this stuff."
Mr Clinton, who hated making quick decisions, was slow in making changes when he came into office.
"That transition is regarded as disastrous," said John Dunbrell, professor of government at Durham University.
"Even when Roosevelt came in, you must remember that the transition lasted until March. Now Obama wants a sense of urgency and does not want to waste this period. And it has been some time since such a major transition. In 2001, everyone was preoccupied by the row over the election result."