For more than four years, they have marched in step through the most desperate and perilous episode of their respective leaderships.
When President Bush mustered his Iraq coalition in 2002-03, Prime Minister Tony Blair was his most vocal ally and recruiting officer. On the most contentious issues of the war – Abu Ghraib, Fallujah, political and military strategy – they have managed to maintain unity. Reinforced by an apparently genuine friendship, the Bush-Blair axis has been the unshakable fulcrum on which the Iraq campaign has hinged.
But now, there is a hint of dissonance in the air. Blair's government is desperate to start drawing down the 7,000-strong British force based in Basra at the same time that Bush is beefing up the US contingent in Iraq by more than 21,000. Lt. Gen. David Petraeus, who was confirmed by the Senate on Friday to head the US forces in Iraq, has said he wants the additional troops in Iraq quickly.
The twang of discord was apparent last week when the US ambassador to Baghdad, Zalmay Khalilzad, hinted at American exasperation over the British eagerness to start withdrawing. "It's clear what our preference would be – the longer we stay together here, the better," he told the BBC.
Members of Parliament said that the impression given was that the allies were no longer in step with each other. "Wouldn't it be better to have a robust exchange of views with the US administration and then implement an agreed strategy?" asked William Hague, the shadow foreign secretary.
Professor George Joffe, a Middle East expert at the Centre for International Studies at the University of Cambridge, says Mr. Khalilzad's words bespeak a rift.
"You can't pretend there is no rift over strategy," he says. "The British are determined to get out of Iraq come what may, whether they have a secure situation in Basra or not. The British forces in Basra, separated between the palace and the airport, are vulnerable to any attempt by a militant group to pick them off.
"And they face a real threat should the Americans move strongly against the Sadrists in Baghdad," Professor Joffe adds. "I can understand the American concerns, and I understand the British anxiety to get out, so there is dissonance."
Some analysts say that Blair has been caught off guard by the sudden change of direction in Washington. When the Iraq Study Group produced its report, advocating a US troop withdrawal by 2008 and a dialogue with Iran and Syria, Blair welcomed it. When Bush rejected the findings and announced his plans for a troop "surge," Blair merely responded that that "made sense."
Lord Tim Garden, a defense spokesman for the opposition Liberal Democrats, said that Blair was wrong-footed by Bush's decision to increase troops. "The British government assumed that [the ISG report] was the new strategy that was to be adopted," he says. "It left them looking flat-footed by the time Bush decided to go in another direction."
Officially, the government says there is no rift, and no timetable for withdrawal, even though they are confident they will be able to hand over Basra Province to the Iraqis in the spring. But privately, ministers are keen to pull at least some troops out for a number of reasons, experts say.
First, troops from an overstretched Army are needed for the fight against the Taliban in southern Afghanistan, where British soldiers have been dying at a rate outstripping the casualty toll in Iraq.
"The British political leadership are desperately keen to reduce the number of British forces in Iraq," says Sir Hilary Synnott, formerly the coalition coordinator for southern Iraq. "There is a greater realization that the burdens on Britain in southern Afghanistan are severely stretching the British Army and, therefore, there is a particular wish to draw down [troops in Iraq]."
Second, polls suggest public opinion strongly favors a pullout. Ever since a top general, Sir Richard Dannatt, suggested last September that the British presence was only aggravating Iraqi sensibilities, the clamor for withdrawal has grown. For the first time, an opposition party – the Liberal Democrats – has outlined a specific timetable for withdrawal of all troops, by October.
"We must go for it because we are now clearly attached to a strategy that the British government and half the US political class do not believe in," says Lord Garden.
A third reason is that Blair's time in office is limited – he intends to stand down in the summer. Joffe says both he and his likely successor, Gordon Brown, are keen to tie up loose ends in Iraq: Blair does not want to leave unfinished business, and Brown does not want to inherit a mess.
Officials argue that it would not be incongruous to have British troops leaving while thousands of American reinforcements arrive. After all, they say, different parts of Iraq need different approaches: Baghdad and Anbar Province need the beefed-up presence. In the south, the British have already ceded control of two provinces to the Iraqis.
Not everyone accepts that rationale. "That argument is becoming difficult to sustain, particularly as everyone is worried that the more robust US rules of engagement in taking on the Shia in Baghdad will have a knock-on effect on the Shia in the south," says Lord Garden. "That could make it more difficult for the British."