John Rentoul: It's make your mind up time, Mr Brown

The Prime Minister's awkwardness is a welcome change from his predecessor's actorliness, but he is faces tough military choices

One of the under-appreciated arts of politics is the management of expectations. So far, Gordon Brown has played it brilliantly. This is partly because the vehemence of his Blairite enemies kept leaking into the open air. One thinks, for example, of the "senior Cabinet minister", who is probably still a senior Cabinet minister, who said, less than a year ago: "Gordon would be an effing disaster as prime minister."

Well, he hasn't been – or, at least, not yet, and the implication of some of the opinions expressed about Brown was that he was so impossible that his flaws would have brought him low by now. Instead, as another anonymous Blairite has been quoted as saying, we have watched him "turn his pathologies into assets". His awkwardness is a welcome change from Tony Blair's stage act. More than expected, it has been hailed as authenticity.

As always, the difficulty of managing expectations is that they can develop a momentum all of their own. There are two issues on which Brown has shifted the balance in his favour, but risks being trapped by the follow-through.

One is the date of the next election. It could still be this year, but prime ministers tend to want a long run of solid opinion-poll leads before going for an early election.

Brown has also only just shaped the story of "the change" from Blair to him: it is a little early to start telling a new story about why that change is great enough to need a new mandate from the people.

But expectations among politicians and journalists are already running strongly towards an election in the spring of next year. Ed Balls, Secretary of State for Children and Brown's closest adviser, noticeably narrowed the planning window in an interview in the Financial Times last month: "Whether the election is in one year or two, it is no surprise that we are thinking about it today."

Any time now, a spring election could be promoted to that category of future events, the Settled Assumption. And then it would be tricky to get out of it without feeding a self-fulfilling cycle of bad news. "Brown postpones election as opinion polls slump." The headlines almost write themselves.

The other issue is that simply by not being Blair, Brown has raised expectations of a different policy on Iraq. So far, again, he has kept his balance as he treads the line between being wrong but wromantic (troops out now) and being right but repulsive (see it through).

There was a wobble over the appointment of Lord Malloch-Brown, who opposed the Iraq war, as a Foreign Office minister. Brown had to hurry to Washington to say how special the special relationship remained. Yet the balancing act went on: he was be-suited and stiff, thus putting a little symbolic distance between himself and George Bush.

Since then, the expectation that the US and Britain will cut and run from Iraq has grown. The Democrats have turned down the heat on the issue as in the course of this month Hillary Clinton pulled far ahead of the anti-war Barack Obama in the race for the party's presidential nomination. Instead, it is Republican voices that have been raised demanding that the troops come home.

That was the reason for President Bush's strangest speech yet, delivered to the national convention of Veterans of Foreign Wars in Missouri last week. When politicians talk about the lessons of history, it is time to start counting the spoons."We can learn something from history," he told. Not after he had finished with it, we couldn't.

It was the first time the President had faced squarely the national memory of Vietnam and the way in which it colours perceptions of Iraq. I do not share the view of Bush as a simpleton, but what a hash he made of it.

"The price of America's withdrawal" from Vietnam, he said, "was paid by millions of innocent citizens" in Vietnam and Cambodia. The idea that Pol Pot came to power in Cambodia because the US withdrew from Vietnam is simply embarrassing. On the contrary, it was American bombing of Cambodia that helped create the conditions in which the Khmer Rouge could take over.

This is revisionism that might make Stalin or Mao blush: that American sacrifice laid the foundations for Vietnam's relatively benign condition today; and that the only thing that Nixon and Ford did wrong was to pull out too soon.

With history as wonky as this, President Bush damaged an important argument that needs to be made. What he was trying to say was that no one should assume that pulling out of Iraq is a cost-free option – either for the Iraqi people or for the rest of the world.

The point is that Iraq is not like Vietnam: pulling out of Vietnam was right, pulling out of Iraq would not be. That is not an easy argument to make. It is hard enough to rally troop morale and public opinion with the cry, "It may be bad, but our noble cause is to stop it being worse." But rewriting history is not the answer.

There is, though, another kind of rewriting of the past going on, on this side of the Atlantic. The assumption that Brown was a sceptic about the Iraq war sustains the idea that there is an alternative history of the recent past – in which Britain stayed out of the war – and all Brown has to do is get back to it.

Even if it were true that Brown had his doubts, if he had acted on them, the most that would have happened is that Blair would have been forced to stand British forces aside from the invasion. But Britain would have sent troops to help with reconstruction, so we would be in roughly the same position as we are today: in Basra with no easy way out.

One of the other reasons why the US Democrats have cooled on detailed plans for withdrawal is that there aren't any. Every group that looks at it, from Baker-Hamilton in the States to the Paddy Ashdown, Margaret Jay and Tom King commission that reported in London last month, makes vague suggestions about talking to the Syrians and the Iranians and then says that it is all very difficult.

What is clear is that the view of the Iraqi people, and their government, has not changed since the invasion: they want coalition troops out, but not yet. And remember what Brown actually said at Camp David: "In Iraq we have duties to discharge and responsibilities to keep, in support of the democratically elected government, and in support of the explicit will of the international community, expressed most recently through UN Resolution 1723."

Those are not duties and responsibilities easily to be shuffled off, yet by his off-text symbolism Brown risks adding to the expectation that this is precisely what he intends to do. Now he is close to a moment of choice when he has to disappoint that expectation – or pull the British troops out of Basra before the Iraqis are ready.