I am one of billions of people who find themselves astonished and delighted by this event. But the election is just the beginning. Few presidents have confronted bigger challenges than Mr Obama. Among that number must be counted two of the greatest – Abraham Lincoln and Franklin Delano Roosevelt. Mr Obama regards himself their heir. The question is whether he can come close to their exalted level.

The new president's agenda is daunting. His country's power is also reduced. Indeed, it was never as great as those who spoke of the “unipolar moment” believed. But the US remains the world's greatest power and only leader. It possesses unmatched assets. The presidency of George W. Bush was a lesson in how not to use them. The Obama presidency must now be the opposite.

Events will shape Mr Obama's priorities. But one such event is already here: the world is entering a recession, possibly the worst since the second world war. Yet he must meet this challenge in ways that preserve what is among the greatest achievements of his predecessors: the open world economy. It was under FDR and Harry Truman, both Democrats, that the US started to lead the world away from the autarkic policies of the 1930s. The US must not now turn its back on the world it shaped. Yet it may do just that, without creative and radical reform, at home and abroad.