By Kim Ghattas
BBC News, Washington
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.
Mr Obama has been reaching out to America's foes
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.
Within a few days of his inauguration, Mr Obama started checking off the long to-do list he had discussed during his campaign.
He announced the appointment of a special envoy to the Middle East to tackle the intractable conflict, declaring that peace in the region was "important to the United States and our national interest [and] important to me personally".
He shifted attention away from a war he opposed, in Iraq, back to the "clear and focused goal, to dismantle, disrupt and defeat al-Qaeda in Pakistan and Afghanistan," a mission started under President George W Bush but which lost steam as the Iraq War unravelled.
He reached out to the Muslim world and started mending America's image around the world, declaring he would close the controversial detention centre in Guantanamo Bay.
He sought to reset relations with Russia - and mark what could be turning points in America's relations with Cuba and Iran.
On every foreign trip, in every meeting with a foreign leader, President Obama has said he wants to listen, not dictate, hoping to set the stage for a more co-operative foreign policy.
"I think it's been very important, the tone that President Obama, Secretary Clinton, Secretary Gates have fashioned," says Wendy Sherman, a former Clinton administration official who is now a Principal at the Albright Group, a global strategy firm.
"It is a tone of leading and listening... [Understanding] that the world is a complicated place [and] the United States alone cannot solve all of these problems," she says.
"But also understanding that the US has a responsibility to lead, accepts that responsibility, will be held accountable for that responsibility.
"So, I think they've gotten off to a tremendous start in probably the most complex world I've seen in my lifetime."
But critics say that President Obama's attempts to reach out to allies to win their co-operation is a gamble that has not (so far) paid off.
Commentators writing about Mr Obama's trip to Europe said it was a success on many levels, but he had still come home empty-handed on issues like European troop commitments for Afghanistan.
So far Mr Obama has delivered plenty of foreign policy vision, but less in the way of substance.
Many experts say that is what the first 100 days are all about - but the gaps need to be filled out soon.
"The administration has launched the country on an important diplomatic enterprise. It now needs to fulfil its vision with a diplomatic plan," wrote Mr Kissinger.
Complicating some of the policy formulations is a fast-changing world.
Crisis and conflicts have erupted in Mexico, Pakistan and even Iraq where violence is rising again.
Elections are changing the political landscape in which the administration has to operate and the interlocutors it ends up with, from Benjamin Netanyahu in Israel to potential new governments in Afghanistan, Iraq, Lebanon and Iran.
Mr Obama made a video message aimed at reassuring Iran
By the president's side is a straight-talking secretary of state with her own star-power and some 60,000 air miles already under her belt - Hillary Clinton.
The administration's new emphasis on diplomacy means the state department is squarely back at the heart of America's efforts to engage with the world, from allies to rivals.
The policy formulation in this administration is a tightly controlled process, closely co-ordinated between the White House, the National Security Council and the Pentagon, with everybody so far seemingly on-message.
The rivalries that plagued the first term of George W Bush have been avoided, despite a cast of very powerful players.
Contrition 'does nothing'
But as he undoes past policies, Barack Obama is also facing criticism, albeit from expected sources.
"I think going abroad and being so contrite for so many alleged sins of the United States is not something that Americans want to see in their leaders when they're travelling abroad," says John Hannah, who was an adviser to former Vice-President Dick Cheney.
He added that the policy of contrition was not even proving effective in changing the behaviour of countries in the world that were of concern to the US, like Iran or Cuba.
President Obama has tried to engage with America's long-time foe, Iran, issuing a video address to both the people and leaders of Iran and calling the country by its official name, the Islamic Republic Iran, to signal that Washington was not seeking regime change.
On Cuba, he has lifted restrictions on travel and remittances for Cuban-Americans, but his handshake with Washington's bete noire, Venezuelan President Hugo Chavez, prompted critics to say the president had to avoid turning engagement into pandering.
The new approach is helping to change the mood and perhaps even the internal dynamic in places like Tehran and Havana, as Cubans and Iranians start to debate the benefits of engagement with the US.
On her first trip abroad, Mrs Clinton said that by engaging "something positive might actually happen, you never know".
"But if you stand at opposite sides of the room and refuse to engage, it's guaranteed nothing will happen," she added.
The momentum and goodwill are still there and the vision has been laid out in the first 100 days, but the next 1,000 days will determine whether this administration will be able to implement its vision and achieve results or whether it has bitten off more than it can chew in a complex world.
The biggest tests are yet to come.