Gordon Brown flew to Boston yesterday to deliver a speech at the John F Kennedy Memorial Library.

The address, we were told, was to be a variation on familiar themes. Having dined with the President and met the three candidates for the White House, the Prime Minister intended to tell his audience that what the world needed most was a re-engineering of its central institutions.

Typical Gordon: dull stuff, anorak stuff, nothing that will make a blind bit of difference in the opinion polls, or in the English local elections. Nothing that will reassure his party, or rescue your mortgage application. Out of touch, you see. Well, up to a point.

You don't need to be a fan of the World Bank, the United Nations, or the International Monetary Fund to see some things from Mr Brown's perspective. Sometimes it helps to doubt the worth of these institutions, and doubt them seriously, to understand how he views his responsibilities.

In the Brownite universe nothing gets fixed, whether famine or global financial stability, unless and until international mechanisms begin to function. You can argue, but you cannot doubt that the issue matters.

The Prime Minister has hammered away this political credo for years, after all. Yesterday, you suspect, it was a rather larger preoccupation than the ditherings of some Parliamentary Private Secretary, or the mutterings of a peer. America is telling itself that the Bush era is drawing to a merciful close. The candidates for the presidency are agreed that multi-lateralism is the way forward, that the United States must once again engage with the world.

So there was Mr Brown in Boston, under the ruddy gaze of Teddy Kennedy, keeper of the family flame, to say: this is how you begin.

That's not the domestic tale, of course. The travelling press pack could have reported that the Prime Minister is on a fool's errand. They could have said that the temptation towards isolationism is too strong for any presidential candidate or policy-maker, far less a foreigner, to oppose. Instead we heard only that the man from HMG is far less well-known in the US than the saintly Benedict or the sainted Blair.

Depends what you mean. It depends, too, on your sense of the parochial. At the US Federal Reserve, the IMF and the World Bank they have a better understanding of Mr Brown, who speaks their language, than they ever had of the photo-exhibitionist Blair. I might judge a man by the company he keeps, but even by that strict criterion the Prime Minister is less troubling than his predecessor.

Mr Brown was an Atlanticist before most people were even aware of the term. All those holidays on Cape Cod, those happy days - each to his own - with the think-tanks, the library stacks and the Democrat strategists left their mark. They also left people on these islands struggling, to take only one example, with the baffling notion of tax credits. They certainly left me wondering about co-option, and the near-instinctive fealty all British politicians seem to develop when the sometimes-special relationship is invoked.

But to say that this Prime Minister is unknown in the US is simply wrong. Hillary Clinton and Barack Obama did not drag themselves away from a bitter contest in Pennsylvania just to be pleasant to some European. George Bush can go through the motions, but John McCain did not likewise head for Washington because he had nothing better to do. They, all three, came to pay their respects to him, the "beleaguered" Prime Minister. That's name recognition.

It is also, you may think, the usual swanning around abroad enjoyed by British leaders who have troubles at home. No doubt the Downing Street team were eager for some handy publicity, as always. But persuading America to aid the reform of international institutions is no minor issue. Implicit in Mr Brown's argument, after all, is the idea that the IMF and the World Bank might operate more effectively if they were not mere instruments of US policy. Implicit, too, is the belief (or perhaps just the hope) that Washington can shed its Bush-Cheney contempt for the UN, lecturing foreigners and vetoes. These are tall orders.

My own view, predictably, is that Mr Brown is probably wasting his time, that self-interest will dominate American policy no matter the occupant of the White House next January. It is difficult, equally, to see how a Prime Minister busily renewing British vows on terrorism, Iraq and Afghanistan can hold much sway when the US takes devotion for granted. The "distance" Mr Brown was supposed to introduce when he took over from Mr Blair is nowhere evident. That only makes the Prime Minister's chosen task more difficult.

Mrs Clinton and Mr Obama both say they want the US "out" (at some time, in some fashion) of Iraq. Where does that leave Mr Brown's loyalty to the Bush cause? Mr McCain, with whom the Prime Minister can "do business", we are told, envisages an occupation without limit of time. Each candidate depicts the supposed war on terrorism in different ways. Which way is Mr Brown's way?

In other words, how can he prevent the arrival of a new American President becoming the means by which British policy, if you can call it that, is judged? Does Mr Brown simply begin a different dance because the Washington tune has changed? If so, his chances of achieving a real reform of those international institutions are remote. Who pays much attention to the pliant client?

Were it not for the fact that his every instinct prevents such a thing, and were it not for decades of unthinking British policy, the Prime Minister could attempt something simple but radical: he could stop talking about the special relationship. America's leaders, of both parties, treat the notion as a kind of comfort blanket. They are sentimental about the ragged old thing when it suits; it saves them from feeling friendless in their darker hours; but they do not accord it much real value.

The Brits are useful. They are reliable purchasers of weapons systems. They are handy providers of intelligence, bases and trade agreements. But they do not act independently, and they do not assert a distinctive British interest.

Clinton, Obama and McCain have treated Mr Brown as an important ally. They recognise a simple truth. That does not mean they will be swayed, if in office, by an ally who is never prepared to put friendship at risk. Recall, if you can bear it, the general bafflement over Tony Blair's inability to deploy his vaunted "influence" over Mr Bush. Is that the relationship Mr Brown means to inherit?

If so, any reform of international institutions will be at a time and in a style of America's choosing. As with all those famous G8 promises, Mr Brown will be left to put a brave face on things. In Iraq and Afghanistan, meanwhile, British acts and British losses will have to be re-explained, yet again, according to the behaviour of the latest person to occupy the house on Pennsylvania Avenue.

The guessing, meanwhile, is that Mr Brown would probably prefer Mrs Clinton, old friend and policy nerd, to the presidential alternatives. But the choice, as he said in Washington, is not his. The choices he makes for Britain are, or ought to be, a different matter.