It was chance that news of the departure of Anji Hunter from Tony Blair's side came in wartime but, as with every move she has made through all these years, it casts light on his character and the politics of the moment. He is the intercontinental Prime Minister, the shuttler from Islam to Christendom, Washington's friend on the hotline, the self-appointed European fixer who calls the others to his table, and yet in these days of his greatest test he is strangely alone. The story of Mr Blair and the war against terrorism is the story of a leader who is discovering how solitary the business of high politics can be.
One day there was always going to be life without Anji as the guardian of his office – though in Downing Street the idea has always carried a slight frisson of fear with it – and the decision that this is the right moment for the old gang to start breaking up points to the changes in Mr Blair in the last six months or so.
Even before 11 September, those closest to him were observing a shift: they believed that it sprang from a deeply uncomfortable election campaign – one in which his relations with Gordon Brown came under new strain – and had made Mr Blair more introspective, a frame of mind which mirrored the obvious physical signs of ageing that were starting to give him a spare profile and a wearier demeanour. Then came war, or something like it. From the moment he was told of the attacks backstage at the TUC conference in Brighton (and concluded in an instant that it was terrorism on a scale that would transform everything) he became a Prime Minister driven, obsessed by the thought of what might lie ahead.
The change of mood forced on him in September matched a sense of unease about the Government's performance. The NHS looked as if it couldn't be turned round properly, even in a full second term; he was irritated by the lack of talent rising through the ministerial ranks and (rightly) blamed himself for it; he was aware that the curse of spin has somehow to be expunged; he was puzzled why it was that for all his talk about the "third way" no one seemed to have provided a convincing explanation as to where it led, least of all himself.
With one lightning flash, all that was transformed into a challenge that now encompassed military action, terrorist threats and a new "world order" that seemed so strange and makeshift that it wiped the slate clean. It was scary, but it allowed Mr Blair in his conference speech in October to map out new ground.
The rhetoric was ripe, and some of his colleagues thought it unwise. But Mr Blair had obviously discovered a way of talking about policy and his ambitions that allowed him to link his domestic instincts (non-ideological and out of step with much of his party's thinking as they were) with a view of abroad. He sounded as if he had discovered – perhaps for the first time in power – his own authentic voice. It scared some of his cabinet colleagues, as well as significant parts of his party who couldn't publicly share his commitment to a long military campaign, and their alarm came from the knowledge that this was not a prime minister flailing around for a theme; this was a leader who had found one.
This conflict has set the leader apart. This doesn't look like a struggle being waged by Jack Straw, Geoff Hoon and Admiral Sir Michael Boyce standing in a circle around the Prime Minister, but by one man. From the start he was naturally drawn to the drama of the moment, and its scale seemed to persuade him that he must become a leader who exhibited utter certainty about the cause. There would be no going back.
He might have to work hard on the Americans to prevent the hawks carrying the war to Iraq and beyond – and that battle is coming closer – but in his justification for action in Afghanistan he behaved like someone who had confronted the arguments for a just war, like a monk in his cell, and concluded that they won. He'd use his feeling for Islam to pour balm on some of the consequences, but he wouldn't pretend that he didn't believe in bombs.
Hence, the solitary Prime Minister. Mr Blair looks now like a man who has drawn in on himself. Intimates reported from the earliest days after 11 September that he seemed possessed by what lay ahead, sensing how dangerous it might be. Now he finds himself enmeshed in a political paradox. Around him, his government is making mistakes, and coming to that moment in its life when the past catches up – the Railtrack muddle, the loud Scottish implosion, a plan for the Lords that promises much trouble, churning unease in the public services and tax rises almost certainly on the way – and yet simultaneously he finds himself the centre of attention in a dozen capitals, with Washington at his feet. The threads of that exhilarating performance on foreign fields are entwined with political dangers at home. But there is no alternative to pressing on.
He cannot know where it will lead. When European leaders came to Downing Street last Sunday (to an ever-expanding table which had Wim Kok arriving an hour and a half late, because he was determined not to be excluded, but left Romano Prodi sitting fuming in Brussels watching the arrivals on television), the atmosphere was much gloomier than the post-prandial briefings would have us believe. At one point, Jacques Chirac put down his fork and said words to this effect: "We know what is likely to happen. A mosque will be bombed by accident during Ramadan. What do we do then?"
Everyone around the table spoke of the coming humanitarian catastrophe, a fact unaffected by whether Osama bin Laden stays in his cave or not, and the problems of electorates that will find, as people have often found in war, that enthusiasm for the military campaign can wane with time. Mr Blair's political potency has been swollen by the demands of this conflict, but it can shrink just as fast if the campaign loses its way in the Afghan snows.
At home, where the idea of an open-ended assault on terrorism is increasingly being subjected to scrutiny, the consequence of his absorption in the campaign and of his new relationship with Bush is as hard for his colleagues to read as it is for outsiders. The central role that he has made for himself has greatly sharpened his political senses, allowing him for example to work on his enthusiasm for the euro with a vigour that was quite absent a year ago, but it has also placed him alone in the spotlight, a figure shining in a harsh glare.
So Mr Blair's future is bound tight to a war whose course he cannot chart. Yet he seems to relish the future. He has always felt a little distant from his party, and anxious to find a way of speaking with a political voice that comes from his ethical beliefs. In the midst of all the danger that now surrounds him, he thinks he has found it. We may be discovering the essence of Mr Blair. But whether it transforms him into a Prime Minister with new confidence and power or whether it is a persona that will haunt him all his days, even he cannot know.
James Naughtie presents 'Today' on BBC Radio 4 and is the author of 'The Rivals', published by Fourth Estate