By Paul Reynolds
World Affairs correspondent, BBC News website
A race is developing to determine whether Iraq can evolve into a stable country before President Bush's term ends in January 2009.
President Bush rallies support for Iraq policy
If the president pulls it off, he can leave the legacy he has been seeking in the Middle East. He would argue that Iraq was the democratic example which justified the war, the cost and the absence of weapons of mass destruction.
If he does not, his presidency will be in large part judged by a failure in Iraq, a failure to produce a democratic government in the aftermath of the dictatorship.
The Iraqi constitution is the latest landmark along the way. But whether the way leads to chaos or constitutional rule remains to be determined.
January 2009 is three-and-a-half years away. It might seem a long way off.
'Four more years'
But General Peter Schoomaker, the US Army's Chief of Staff, told the Washington Post recently that the army was planning for four more years in Iraq.
"We are now into our '07-'09 planning," he told the Post.
Gen Schoomaker: four more years?
This is quite revealing though not surprising. Military planners have to prepare for the worst, and the general says that is what he is doing.
This will not stop the administration from hoping, indeed preparing, to draw down some of its troops, who currently number some 138,000, next year.
But it does indicate that the US presence in Iraq could extend beyond Mr Bush's second term.
The president has been making speeches to rally faltering support among the US public and to try to reassure people that not only is he is holding to the course, which few doubt, but that the course is a clear one.
He is pitching his argument in terms of protecting the homeland.
"Our troops know that if we do not confront these evil men abroad, we will have to face them one day in our own cities and streets," he said in a recent speech.
The constitution is supposed to represent one of the final stages of Iraq's development as a democracy. It should be followed by elections in December and a fully constitutional government by the end of this year.
However, it is being criticised by Sunni leaders as opening the way to the break-up of the country and it is possible that it will not be approved in a referendum which has to be held by 15 October.
It can be blocked if three of Iraq's 18 governorates or provinces vote against it by a two-thirds majority. The Sunnis, it is reckoned, could get that vote in at least two provinces and maybe in the vital third. Many Sunnis are already registering as voters, simply to vote against.
If the constitution fails to win approval, the whole process starts again.
The National Assembly, elected in January, would be dissolved and new elections held in December, with another year being given to try again on a constitutional text.
This is Plan B and it might not be such an unattractive option if it allows Sunnis to rethink their earlier boycott, take part in new elections and then negotiate from greater strength.
But equally, it might simply give more time for the country to fragment.
It is an achievement that this has not happened before now, under the violence of an insurgency whose power was not predicted and never planned for.
But it is also an achievement that gives some hope it will not happen.
Iraq was always an unlikely grouping of its three main elements - Kurds, Shias and Sunnis.
The British put the place together after World War I from three leftover provinces of the Ottoman Empire.
Those the British have joined together have often split asunder or warred among themselves. On the sub-continent, Pakistan was split off from India (by the British but only after fighting among the peoples); Nigeria had a civil war and Cyprus remains divided, to name but three places.
So far at least Iraq has not joined that list.