What Mr Blair must tell the President and the Congress in Washington today

He should not mince his words when pointing out just how urgently the US needs to win back support in the Muslim world

Tony Blair's visit to Washington today will be high profile but brief. Maybe that's just as well. For as he well knows, the warmth of the reception he can expect from Congress is hardly going do much to ease his troubles at home. The fall-out of the war in Iraq isn't his only problem. But it is still the most serious, and if anything, is underlined by the growing unrest in the US over the use of intelligence in the run-up to the war. The question is whether he can do anything about it, instead of just hoping it will go away now Parliament is packing up for the holidays.

Jack Straw proffered yesterday a robust, if lawyerly, defence of the case against an independent inquiry in the Commons. He is helped, of course, by the narrowness of the remit the Opposition seeks to impose on any such inquiry. The more narrowly this focuses on the exact handling of the intelligence evidence used in the September and February dossiers, the more it strengthens the Foreign Secretary's argument that the matter can safely be left to the Commons intelligence and security committee. The point, of course, about a full-blown inquiry is that it would discuss the use - and reliability - of intelligence assessments in a much broader context, just as Sir Richard Scott was obliged to consider the question of arms to Iraq in the much broader context of British foreign policy. For underlying the furore over the dossiers is the much more political question of how, when and why the decision to go to war was made - the decision which Mr Straw repeated to the Commons yesterday "is as justified today as it was on 18 March."

Above all there is the question, way beyond the intelligence and security committee's remit, of what happened when Mr Blair met George Bush in Camp David in September 2002 - whether the Blair government, having agreed with the US (for, let us remember, some very good reasons as well as perhaps some bad) that completing the unfinished business from 1991 was desirable, it then allowed itself to be persuaded too easily that weapons of mass destruction (WMD) would provide the casus belli which it needed to internationalise the conflict through the UN and legalise it in the UK.

One interpretation, now widespread and given some credence in Peter Stothard's account of the Prime Minister's analysis in September 2002 in his illuminating book on the run-up to the war, is that Mr Blair did think war was inevitable and then determined to legalise and internationalise it. This doesn't mean that he lied; indeed there is strong evidence that he - and other ministers such as Peter Hain - were seriously perturbed by the WMD evidence going back well before 11 September. But it may mean that closer and more rigorous scrutiny might have thrown into question whether the evidence justified war, with hugely unpalatable consequences for the US-British relationship if it didn't.

The opposing case, put with some force by those close to Mr Blair, is that a deal was indeed made at Camp David. Mr Blair would support a war, but only on the condition - agreed in return by Mr Bush - that Saddam Hussein did not back down and make a clean breast of the weapons that everyone, the anti-war governments on the UN Security Council included, believed he had (and which, they insist) may well still turn up. If this is true then it's hard to see what the Government has to fear from some form of statutory inquiry.

One of the weaker arguments used by Mr Straw yesterday was the length of time a judicial inquiry could take. Ministers have a point when they say that the argument about WMD can't fully be resolved until the International Survey Group (ISC) has finished its search. But that could take every bit as long as a judicial inquiry. Mr Straw warned the Commons yesterday - arguing, of course, against it - that a Scott-style inquiry would "kick this issue into the long grass for several years" The problem with that argument is this: given that such a development would certainly be in the Government's political interests, it suggests, whether fairly or not, that it has something to hide by refusing it.

The Government would do well to start thinking about how to reverse its opposition to a full independent inquiry, perhaps after the ISC reports in September. If a war waged by a divided alliance in unprecedented circumstances, in which 43 British soldiers have died, doesn't deserve a full post-mortem examination, one is bound to ask what does?

The other question concerns how Mr Blair can make the US/UK relationship work for him at home, as well as for Mr Bush.This depends initially on how he handles the meeting today. There is palpable impatience in Government that Moazzam Begg and Feroz Abbasi, the British prisoners in Guantanamo facing a military tribunal, are the subject of intense focus. It must be very irritating, both to be sure that they are guilty and that they probably wouldn't be convicted in a British court if repatriated. But that's not quite the point. For Mr Blair will tell Congress today that US values of freedom, democracy and human rights are universal and not relative. This goes to the heart of the argument over Guantanamo.

Once the US's own treatment of human rights is called into question, its tenure of the moral high ground is threatened - however horrendous the crimes may be in the eyes of the home country and the rest of the world. The heinous nature of the crime does not, cannot, justify lowering the threshold of proof. Some form of concession may well be announced in Washington today - Mr Bush, not for the first time, seeking to help out Mr Blair in the face of his domestic difficulties. Whether it goes beyond the merely cosmetic remains to be seen.

Another question is the tone Mr Blair adopts when he addresses Congress - now defined as the main purpose of his short, six-hour visit. Having listened at the weekend to some rather sharp criticism of the neo-Conservative right in the US from his old friend Bill Clinton, Mr Blair should not mince his words when it comes to pointing out just how urgently the US needs to start winning back international support - not least in the Muslim world.

Whatever his deep troubles at home, he has a pretty rare opportunity to use his influence to shame those in Congress who will seek to baulk at what British officials continue to insist is the President's genuine commitment to the Middle East peace process. If by the time he leaves town he he hasn't made those US legislators who hope that Ariel Sharon is only kidding when he says that he too is serious at least a little angry, he won't have done his job.

None of this is going to disperse the clouds that will continue to hang over the Blair premiership in the coming months. Agonies within Labour over public service reform are going to dog him up to the party conference and perhaps well beyond. But evidence that he can challenge the President - in substance and not just ritually - as well as praise him would certainly help at home. And right now he needs all the help he can get.

d.macintyre@independent.co.uk