Robin Cook: An awkward question for Blair: who do you want to win the US Presidential race?

Their difficulty is that Mr Blair is totally identified with George Bush over Iraq, the most divisive issue in both countries

Just who will Number 10 be rooting for in the American race to the White House? A relevant question as the shift in our strategy on Iraq from containment to invasion revealed that regime change in Washington can have a bigger impact on British foreign policy than any debate at Westminster.

And a timely question, as on Monday the Democratic primary in Iowa goes to the polls. Well not exactly to the polls, but Democratic voters will go to village halls to caucus over their candidate, not unlike Labour selection committees in the days before one member, one vote.

It is also a more pointed question after a week in which the biggest political story stateside was the revelation by Paul O'Neill, George Bush's former Treasury Secretary, that the conquest of Iraq had been Topic A for the Administration from day one. In itself, this was not news to anyone who had followed closely the long right- wing lobbying for war on Iraq. What made the intervention of Paul O'Neill sensational was the corroboration from a member of the inside circle of what many on the outside had long suspected.

For Number 10, the implications are deeply uncomfortable. According to his former Treasury Secretary, George Bush was from the start of his presidency saying about an Iraq invasion, "Go find me a way to do this". But over in London, Tony Blair insisted until the last minute that no decision had been made and the inevitable launch of the invasion by the White House was a reluctant response to a real and urgent danger.

Downing Street's hope is that Iraq will fade as a political issue after Lord Hutton publishes his report in a couple of weeks, but the reality is that the US Presidential election may keep it a matter of controversy all the way to polling day in November.

Certainly that will be the case if Howard Dean becomes the Democratic candidate. His lead over his rivals may be narrowing, but that should not obscure his phenomenal achievement in coming from nowhere to front-runner. Even now, he is still ahead in the polls, has more volunteers than any of his rivals, and has by far the biggest campaign fund.

In contrast to the vast war chest of the Presidentfrom big corporate business, Howard Dean's funds are the product of thousands of small citizens, making modest donations through the internet. The key to his popularity and to the enthusiasm of his supporters is simple. He spoke out in opposition to Bush's war when most of his rivals were voting for it in Congress.

I have a suspicion that Number 10 is not looking for the same quality in the Democratic candidate. Their difficulty is that Tony Blair is totally identified with George Bush over Iraq, which has now become the defining and most divisive issue in the domestic politics of both countries. Yet they can hardly be seen to support a US President who has torpedoed UK foreign policy priorities, from the Kyoto Protocol to agreement on fair trade.

Nor is there any prospect of Tony Blair achieving a meeting of minds on progressive politics with anyone in a US administration that is slashing tax on the wealthiest and paying for it by equally savage cuts in assistance to the most vulnerable. If it were not for the Iraq war, the clear interests of the British government would lie in the election of any of the rival candidates queuing up to challenge George Bush. Any of them offers the possibility of a return to a multilateralist framework in foreign policy and a resumption of a progressive dialogue on domestic policy.

At present, though, the contest between those rivals threatens to damage the chances of any of them succeeding. Deep in the sanctum of the White House, Karl Rove, President Bush's policy adviser and eminence grise, must by now have a full filing cabinet of quotes by rival Democratic candidates savaging each other, ready for recycling once he knows which of them has won. The new American technique of negative campaigning, combined with the old American system of primary contests, is making the process of selecting the candidate damaging to his chances of subsequent election.

As the front runner, Howard Dean has come in for more stick than any of the others and this week objected to being treated as a pin cushion. The willingness of many in the media to believe that he is prone to gaffes seems rather facile. His statement that the capture of Saddam has made the US no safer does not seem much of a gaffe, more a statement of the obvious. Even in Iraq, it has not made US forces any safer. The main cause of the welcome reduction in US casualties is not that resistance has slackened, but that US patrols have been more than halved precisely because it is not safe for them to venture out and not safe for the administration to risk. Howard Dean should command respect precisely because he has made an open challenge to US strategy on Iraq. As a result, American voters can now witness an honest debate about the merits of invasion.

This contrasts favourably with the position at Westminster where Michael Howard is still struggling to reconcile his party's support for the war with its unpopularity. At least Howard Dean can claim consistency in warning from the start that the invasion of Iraq was unwise, which will increase his appeal if the Bush exit strategy runs into trouble. This week's protests by Ayatollah Sistani on behalf of the Shia majority, and yesterday's large demonstrations in the British sector demanding elections, underlines the challenge of putting together a consensual, representative government in Iraq. For President Bush, these objections are awkward not just because it is hard to see how a representative government of any kind can be formed without the support of the majority ethnic group, but because what the Shia are demanding are democratic elections. It was precisely to deliver democracy to Iraq that we were told America invaded the country.

In truth, there is no insuperable problem to elections in Iraq. The only benign consequence of the ruthless repressive state administered by Saddam is that there are reasonable records, notably for food rations, of who are citizens.

The compelling consideration for Washington against elections is that the Shia would win. Hence their invention of a more pliable system of representation from local groups, not that unlike the Iowa primary caucuses in their complexity and openness to lobbying.

Any problem for US strategy in Iraq will become a problem for President Bush in the US elections - especially if his opponent is Howard Dean. This will test to the limit the diplomatic skills of Number 10. They need to avoid being sucked into the US contest by aligning themselves with the President.

A year of abstinence from prime ministerial visits to the Crawford Ranch or other cosy photo-ops with George Bush is a precautionary prescription. After all, the other candidate got more votes than George Bush last time, and he might do it again this November.