Sometimes American politics can seem distinctly odd to an outsider. If both houses of the British parliament passed votes demanding a foreseeable end to a disastrous war, no Prime Minister could shrug the matter off with the equivalent of: "Get stuffed."

On the other hand, Americans are entitled to look askance at a system, if that's the word, under which Britons are dragged off to wars with precious little in the way of scrutiny, accountability or coherent explanation. On neither side of the Atlantic is democracy perfected. But you knew that.

Nevertheless, next Tuesday, May 1, George Bush will receive a Bill, passed by Senate and House of Representatives alike, making £50bn of additional funding for the Iraq occupation conditional on a timetable for American troop withdrawal. By no coincidence, that day will also mark the fourth anniversary of the President's decision to declare victory and "an end to major combat operations" in the region. Tasteless jokes are optional.

Bush will veto the legislation, of course. That is his right, and he has no other realistic choice, short of resignation. Even with majorities in both houses, the Democrats will, meanwhile, fail to have the veto overturned. That would require a vote by two-thirds of the Senate and the opposition party has no chance of mustering the numbers. The troops will not begin coming home by October 1. The Democrats can live with that, for now.

Bush is in a real and serious battle on the home front. In a televised debate this week, the eight Democrat presidential contenders each declared a determination to get American forces out of Iraq. Even Hillary Clinton, who voted for the war and who has attempted to sit on the fence while the posture became excruciating, said if Bush wouldn't withdraw the troops, she would. The impending long election campaign is being defined by the debacle.

So much was inevitable. When 200 innocents can be killed in a single day, when a suicide bomber can penetrate the Iraqi parliament itself, when the American (and British) death toll rises inexorably, a keen interest in bloody futility becomes obligatory. When Muqtada al-Sadr's half-dozen Shia ministers quit the government of Nuri al-Maliki, abandoning the idea of national unity, and when America's own ambassador to Iraq wonders whether the hand-picked Prime Minister is "up to the job", a "troop surge" begins to seem less than rational.

In losing Iraq, Bush has lost a clear majority of his own people. In forfeiting trust for the sake of an unconnected adventure, he has forfeited what was once deep international support for his war on terror. American opinion is obsessed with these facts, and with the question of what can be done. With the White House soon to be at stake, it has become the paramount issue of the day, and the debate is feverish.

But in Britain? In Britain, there is a strange, stupefied silence, broken only by the muttering of generals and royal aides who have worked out it may simply be too dangerous to allow Prince Harry to serve in Iraq. No doubt the public will understand the fear, but then wonder why one serving officer should be different from any other serving officer. The public might also conclude, simply, that if things are so perilous, and growing worse, the great campaign is a clear, unadulterated failure.

So where is the political echo? It is as though we have each settled on our opinions, and left it at that. Most observers of the Scottish elections have, therefore, concluded Tony Blair and Labour are about to be punished, in exemplary style, for Iraq. I don't dissent from the view. As with Bush, a charge of dishonesty has been attached to the charge of failure, and Blair's party will pay a heavy price.

That, though, isn't half the story. America is debating the need and the mechanisms for withdrawal. America is asking itself about life after Bush. Yet official, political Britain has not even begun to contemplate an equivalent future. No-one is talking. Blair will be gone in a matter of weeks, long before his American friend. Do we simply wait until a new administration in Washington decides to call it quits, or do we prepare? Cursing the war is right but easy, the rest is hard. Where's the leadership?

When he was wallowing in simplicities and certainties, Blair savoured his own nobility. He is history now, bar the rude shouting. Alex Salmond and others among Labour's opponents can claim an honourable record of opposition to the Iraq adventure, but the SNP won't get the troops out next Friday, or on any Friday thereafter before a new American President is sworn in. Meantime, so we hear, Gordon Brown will become our Prime Minister.

It makes for an interesting conjunction. Brown's sympathies, and much of his political history, connect him with the Democrats. It would suit him, equally, to put distance between himself, the Blair legacy, and the Bush White House. What better riposte could the new Prime Minister offer to his Labour enemies when they accuse him of losing Scotland? Simply this: Iraq destroyed us, Iraq wasn't my idea, and here's what I propose to do next.

Only a unilaterally imposed timetable for British withdrawal would truly answer the case, and Brown has evinced no appetite for that. In fact, he has said next to nothing about Britain's biggest crisis in a quarter of a century. Nevertheless, a new Prime Minister would benefit from asserting that, in matters of war and peace, Britain still has opinions of its own. The alternative is a continuing disaster, political suicide in slow motion, the last of Blair's victims.

No-one should imagine promises made by Hillary Clinton during a campaign will be confirmed, necessarily, by a President Clinton. Withdrawal from Iraq will be fiendishly difficult and horribly messy. The first woman President will be tempted to show she can be as tough as any man, especially if the man is called Bill. But the tide has turned. America wants the nightmare ended. Yet here Britain sits, on the sidelines, detached from the debate. Brown cannot afford even the appearance of such impotence.

I don't say he will act; I only say he would be foolish to duck the challenge. The tale of Iraq has reached the point when the miscreants fall out among themselves, when fingers are pointed and names are named. Next week, for example, George Tenet, the former head of the CIA, will give his own version of events in an attempt to salvage his reputation. In his book, At the Centre of the Storm, he will say bluntly that Vice-President Dick Cheney and others in the White House demanded an invasion of Iraq without a "serious debate" on the threat, if any, posed by Saddam.

Of "significant discussion", equally, there was none, says Tenet. Truth was not the object of the exercise. The American people know it now; the British people, most of them, believe it. The difference is that, in the US, the people are witness to a political class fighting tooth and nail over possible solutions. Gordon Brown should pay Britain the same respect, for his own sake and ours.