President Obama celebrates his 100th day in office and by anyone's standards he has been busy. On the domestic front he has secured a $789bn recovery package, confirmed a plan to bail out the auto industry, sealed the fate of Guantanamo Bay, opened the way for stem cell research, geared the nation towards radical climate change legislation and dared to suggest the atomic bomb must go.

Internationally he has overhauled foreign policy from Cuba to Afghanistan, ventured into a new relationship with Iran and even risked dabbling in matters European by endorsing Turkey's entry into the EU.

As the reaction to his presence at the London G20 confirmed, his confidence, energy, charm and humility in offering a fresh approach, (used to such great effect during the election campaign), helped heal wounds, draw a line under the last administration and earn respect with world leaders who had distanced themselves from an arrogant and unpopular America.

Yet with little actually achieved, cynics might say that it has been a 100 days of triumph of style over substance. And anyway, after Bush, it was not a hard act to follow. In addition the continuing civil war in the Republican Party means there is still no opposition to hold him to account.

But even in this short time Obama has done more than just outshine his predecessor. He has profoundly set America on a radical change of course, redefining what America is about, what the nation aspires to be and how the world perceives it. A more responsible, more respected and more resolute nation.

Even at this early landmark in time this is already proving to be the most serious and challenging presidency in living memory, testing the limits of the possible. The real game of governing is of course about to begin. But has already achieved the single thing many Americans were looking for and what Gordon Brown has never been able to realize, namely that Churchillian spirit that we will get through this. Even though times are tough, even though life is difficult - there is indeed hope.