The BBC's Washington bureau has been tracking the news during Barack Obama's first months in office, in a
daily 100 days diary.
Now, on the 100th day of his presidency, they sum up some of the key developments since his inauguration.
JONATHAN BEALE: TERROR TACTICS
They were among his first big decisions - to close Guantanamo, shut down the CIA's secret prisons, and end the intelligence agency's "enhanced" interrogation programme.
In one sense, they had an immediate result - breaking with the Bush administration and improving America's tarnished global image.
But 100 days on, the goal of closing down the detention centre at Guantanamo still seems some way off, and the decision to denounce the past techniques of the CIA is kicking up a political storm.
First Guantanamo - so far Britain has taken back Binyam Mohammed and France has taken another, which still leaves around 240 detainees.
At the time of writing, US Attorney General Eric Holder is travelling Europe trying to persuade countries to take some more.
A number of governments first want to see how many detainees America itself will take.
Finding a home for a handful will be the easy part; what to do with around 100 detainees from Yemen, more difficult.
Send them back and Dick Cheney will see more proof that this administration is weak on terror.
The rush to close Guantanamo, and to denounce the CIA's past has left this administration exposed on national security.
For Barack Obama the bottom line is standing up for America's principles. For many Republicans it's all about keeping the country safe.
You get a real sense of the dilemma in the row over the release of the CIA "torture" memos.
The president is now caught between the human rights and civil liberties lobbies, who are demanding prosecutions on the one hand, and members of the intelligence agencies - past and present - who feel betrayed on the other.
President Obama may have thought coming clean was the best policy. But in reality, he's now going to be spending the next 100 days - probably more - arguing over how much of America's dirty laundry should be shown to the rest of the world.
All the while, Dick Cheney is primed and waiting to say, "I told you so," if one of these decisions backfires and does make America less safe.
JAMES COOMARASAMY: ENERGY POLICY
Energy policy is one of the areas where the Obama administration has already offered a stark break with the past.
After years of US reticence about tackling climate change, the White House now has an occupant who is committed to taking a global lead in reducing greenhouse gas emissions.
President Obama has instructed congressional Democrats to draw up legislation that would establish a cap and trade system, allowing companies who continue to pollute to trade carbon credits with those who take more rapid steps to use cleaner energy.
The ultimate goal is to reduce greenhouse gas emissions by more than 80% by 2050.
The president has also linked the fight against climate change with the battle against unemployment.
He has appointed a special advisor to help reach his goal of creating millions of "green jobs" - blue collar jobs with an environmentally-friendly goal.
But the good intentions have already run up against obstacles in congress.
Democrats have delayed further action on a big climate change bill they'd hoped to have in place this week.
The reason: disagreements, not just between Democrats and Republicans, but between Democrats who want to push ahead faster and those from oil, gas and coal-producing states, who are worried about over-burdening industry at a time of economic crisis.
There is one thing that Mr Obama has up his sleeve: the recent landmark ruling by the US Environmental Protection Agency that carbon dioxide emissions do pose a threat to human health.
If the politicians won't legislate, the administration might have to regulate.
RAJINI VAIDYANATHAN: FIRST FAMILY
The first 100 days of the Obama presidency have been about more than just a president - they have told the story of the first African-American family in the White House, a very young one at that.
The interest in the First Family has been as much a part of the story as the president's policies.
interest in Michelle Obama
as a separate entity, and the addition of a White House pet, Bo the dog, are testament to that.
The Obamas have tried to portray themselves to ordinary Americans... as a family people can relate to - be it Mrs Obama's credit crunch chic when she chooses to wear high street clothes, or her call to Americans to plant their own organic vegetables, just as she is doing in the White House garden.
Of course their status and the trappings of power mean they're anything but ordinary, but Mrs Obama is always keen to point out that she has to juggle the demands of motherhood and work like anyone else.
The juxtaposition to all of this is that the First Family are the biggest celebrities in the world - Stevie Wonder played in their house and A-listers are queuing up to meet them.
As Barack and Michelle Obama sashayed down the red carpet at Downing Street for a G20 dinner, you could've mistaken them for an Oscar night entry - the papparazzi are always close by.
But almost all of the photos we see of the family, be it the children's swing in the garden or the playful pictures of them walking the First Dog Bo, are carefully orchestrated.
The high approval ratings for both Mr and Mrs Obama show that the love affair the American public have with the First Family is still going strong.
MAX DEVESON: APPROVAL RATINGS
Barack Obama's honeymoon is over - but not so you'd notice.
His approval ratings were pretty high at the beginning of his presidency, and have sunk only slightly as he reaches his 100th day in office.
While individual pollsters' results vary, they all indicate the same trend: the number of people expressing approval of Mr Obama has decreased somewhat since January, while the number of people expressing disapproval has risen.
And the growth in disapproval has been sharper than the decrease in approval.
Clearly some of those who - perhaps carried away by the pomp and ceremony of inauguration day - initially expressed their support for the new president have revised their views on closer scrutiny of his actual policies.
On average, Mr Obama's support has dropped by around 10 percentage points, while disapproval is up by some 15 points.
That said, Mr Obama's approval rating has remained essentially unchanged since early March.
The ABC/Washington Post poll has been the most favourable to Mr Obama. It gave him an approval rating of 80%-15% around inauguration day, falling to 68%-26% in its most recent survey.
Rasmussen has been the least positive for the president: it had him at 65%-30% in January, and 55%-44% today.
Gallup's results have been somewhere in the middle. According to their polls, Mr Obama had a 67% approval rating in January, which dropped to 61% earlier this month, but sprung back up to 65% on his 100th day in office.
All three polls indicate that Mr Obama still has the support of the majority of the country as he heads into his next 100 days.
JAMES COOMARASAMY: HEALTHCARE REFORM
Amid all the other huge economic problems he's tackling - rescuing the US banking system, deciding how far to rescue its car industry - President Obama has been careful to stress that healthcare reform cannot wait.
Central to his ambitious agenda is a belief that improving the health of the US economy partly depends on improving the health of the American people.
In his address to a joint session of congress in February, Mr Obama said the cost of healthcare was weighing down "our economy and our conscience".
So, in his budget proposal, he set aside $634bn (£428bn) over 10 years to pay for reforms designed to significantly lower the number of Americans without health insurance. That figure is currently thought to be around 46 million people.
As part of the consultative process, he's organised a healthcare summit at the White House, where he assembled the various bodies with a potential stake in the reforms - employers, unions, healthcare professionals, insurance companies.
It was a clear attempt to avoid the appearance - which proved fatal to the Clinton healthcare initiative - of a secretive plan being cooked up behind closed doors.
He has been handicapped by the withdrawal of his first choice of Health Secretary, Tom Daschle, over tax issues.
Many health professionals, in particular, had of hoped that having the former senate majority leader as the president's point man on the issue would smooth the legislative process.
Republican opposition to greater government involvement in healthcare - something they label "socialised medicine" - means that process will not be easy.
The details of the bill are still being worked out, but the Democratic majority hopes to have something ready by June.
The recent news that the White House wants senate Democrats to use a congressional procedure to override Republican opposition has given a sense of the scale of the political challenges the president is expecting; and of his determination to overcome them.
GREG WOOD: ECONOMIC TEST
You cannot accuse President Obama of lacking energy when it comes to economic policy.
But effectiveness is another matter.
His first 100 days contain at least one notable achievement - the $787bn (£539bn) stimulus plan.
The American Recovery and Reinvestment Act, to give it its proper title, was signed into law by the President less than a month after he took the oath of office.
It is the single biggest peacetime spending initiative in US history and was passed in record time.
But it failed to gain the bi-partisan support in Congress that President Obama was looking for and has become a rallying point for Republican opposition.
KIM GHATTAS: FOREIGN POLICY
Barack Obama's presidency has been dominated by the economic crisis, but that has not stopped him from trying to launch a massive recalibration of US foreign policy.
The breadth of issues he has tackled in this short time is unprecedented, prompting former Secretary of State Henry Kissinger to write recently in the Washington Post that "the possibility of comprehensive solutions is unprecedented".
There is no guarantee that any of it will lead to success over the next four years, but the new administration is aiming high.