One very famous face was absent at the State of the Union address to Congress last week. The missing person was Hillary Clinton, and the silly chatter predictably started. Was it a deliberate snub? In fact, a glance at the diplomatic calendar would have instantly dispelled such notions. The US secretary of state was away in London, attending important talks on Yemen and Afghanistan.

Even so, the non-event was revealing. It spoke to Clinton's celebrity and to the political ambitions that some cannot believe she does not still harbour. And it also reminded us that right now she is a hardworking, constantly travelling secretary of state who seems to be doing a pretty good job.

Such judgements of course must be cautious. US foreign policy is set by the White House, and the most effective secretaries of state are those who combine deal-making savvy with closeness to the president. In the end, a secretary of state's successes and failures are those of the president.

But Clinton is putting her own imprint on US foreign policy. She constantly emphasises "smart power", which relies less on military might and more on diplomacy. She has used her celebrity to focus attention on issues such as womens' rights and the global fight against poverty and hunger. She has launched a four-year review to boost the state department's resources and staff, and put policy planning on a longer-term basis. She has worked smoothly with the big-name envoys appointed in key policy areas, including Richard Holbrooke for Afghanistan/Pakistan and George Mitchell for the Middle East. When she first took over, there was talk of Clinton's voice being drowned by a clash of other mighty egos. But no longer.

"Hillary and the envoys have shown loyalty, consistency and cohesion, and the structure has worked," one senior ambassador in Washington noted. What hasn't worked, of course (or at least not yet), are the policies, as the overlapping, seemingly in­tractable crises in Iran, the Middle East and Afghanistan attest.

But Hillary must be doing something right. Polls consistently show her to be the most popular member of the government. She is, of course, lucky that her job keeps her away from America's dysfunctional domestic political system and the deeply unpopular Congress in which she used to serve.

Even so, Obama right now would die for her 65% or 70% approval rating. From there it is but a small step to speculation about a new Hillary bid for the White House in 2012.

But the last chapter in her political career has probably begun. Even if Obama asked her, she told an interviewer, she could not imagine serving eight years as state secretary. The job was simply too exhausting. She spoke fondly of life afterwards, "of reading, writing, maybe teaching". And being a successful one-term secretary of state is surely preferable to no presidential term at all.