There is that moment when the snackering sound of a rifle being cocked makes you pay attention. And three camouflage-uniformed members of the new Iraqi National Police had just cocked their AK assault rifles. The half-dozen grey-patterned US soldiers standing protectively in front of the man in the grey shirt were now paying attention. Later, they said they thought they were about to get into what the US military calls an "escalation of force situation". But, with a lot of shouting and pushing, and a deal of finessing by Lieutenant Ford and his interpreter, the situation was eventually defused.
Last weekend, Channel 4 News's Nick Paton Walsh and I were in the district of Shula, right beside the famous Umm al-Mahare ("Mother of All Battles") mosque in north-western Baghdad, travelling with a search patrol as it cleared the half-built villas dotted over the marshy land around the mosque. The morning's work had been un event ful. Around eleven, the Iraqi police patrol accompanying the platoon from the US 2nd Battalion, 12th Cavalry Regiment announced that we had to look for a car. Apparently, there were "terrorists" in an Opel or Mercedes-Benz on the other side of the mosque. The joint patrol rapidly set off across sheep-riddled wasteland. Within minutes, the lead Humvee had stopped an Opel. Inside were two men, well dressed in the smart casual clothes of the Iraqi middle classes.
It quickly became obvious from the shouting and waving of weapons that the Iraqi National Police felt these two should be terminated. Realising this, the American lieutenant moved his men into defensive positions around the detainees, having to extricate one of them from a pasting being administered by several police officers. This quickly put him at odds with his comrades-in-arms. Later, he said he had feared there was a moment when they were about to be attacked by the police patrol.
At the time, I felt sure that the only people in danger were the detainees, but the US soldiers were really spooked. The lieutenant explained that the Iraqi police had become agitated when the men, on being questioned, produced documents showing that they worked for US intelligence. They were also Sunni. In a Shia area. And had been apprehended by an INP patrol that was completely Shia.
That is why this little incident is so revealing and showed the problem of Iraq in a microcosm. I have been reporting from Iraq since the Iran-Iraq war of the Eighties, but more recently during the latest upheaval since 2002. I witnessed the "Shock and Awe" air campaign from a balcony of the Palestine Hotel. That extraordinary display of firepower killed hardly anyone, and the actual war itself killed very few.
But the evil genie unleashed by an inept execution of regime change in Iraq has been horrifying to watch. Since I was last here in December, the Shia-dominated government has rushed Saddam Hussein to his ignominious end and the place now seems somehow hollow.
I would never mourn the old killer, but it seems obvious that he and his Ba'ath Party thugs held this secularised Arab nation together, as well as in thrall. Now the nastiness is barefaced, the bitterness of the oppressed is expressed in their revenge, and criminality is given free rein.
As is now commonly acknowledged, the invaders have found themselves in something of a quandary. Resistance to the "liberation", initially laid at the door of the former Ba'athists and al-Qaeda, changed subtly after the White House forced Iraq into an election that returned a Shia majority. The newly legitimised authority of the majority has since allowed the age-old fight between Sunnis and Shias to flare up - to the point where a death toll of "only" 1,531 in February this year is seen as an improvement on the monthly figures for the second half of 2006.
As the incident last Saturday showed, increasingly, most Sunnis need the US to stay so that the democracy the Bush administration bequeathed the country doesn't turn out to be a death sentence for them.
Lieutenant-Colonel Nikolas, commander of the 2nd Battalion, says the Baghdad security plan designates Shula as a quiet neigh bourhood requiring only an "economy of force" to police it. But then it is not run by the US troops who patrol there daily, nor by the INP, nor by the Kurdish Iraqi army battalion stationed there. Shula is run by Moqtada al-Sadr's Mahdi militia, who, for the moment, have hidden their weapons and changed out of their black fatigues while the Baghdad security plan proceeds.
Time is on their side. They need the plan to give the US the sense that things have calmed down. They also need the US to beat the Sunni groups, such as al-Qaeda, which fight both of them, while they consolidate their turf. Then, when the US begins to withdraw, they can finish the job of making sure that the Sunnis are completely broken.
Lieutenant Colonel Nikolas is under no misapprehension. He knows he is being used. But he's an officer with the lives of his men at risk and a job to be done, so he's going "hammer and tongs to sort out this area" south of Shula, along the Jordan-Syria highway out to Abu Ghraib and Fallujah. Every day, one of his companies patrolling the area comes under attack. They believe they have dislodged resident al-Qaeda Sunni insurgents from the blocks of shoddily built middle-class villas, but the attacks, although reduced, have not stopped.
At the same time, Nikolas has stabilised a "creeping front line" where the Mahdi Shia militia was pushing south from Shula into Ghazaliya in a spate of ethnic cleansing.
"They [the Sunnis] needed us to stop them being pushed out by the Shias from the north. We're doing that. But their brethren to the south make it real difficult," he says referring to the insurgent attacks from near the highway.
Thus, at every level, Americans are having to come to terms with the reality they have created. From Lieutenant Ford, protecting two men on the ground in the salt marshes of Shula, through Colonel Nikolas, working in an area where whole districts have to be protected, to the president in the White House, who has to juggle the complexity of power politics between Sunnis and Shias at an international level, the problem remains the same. It's only the scale that differs.
"It seems we're caught right in the middle of this," said Lieutenant Ford.
Tim Lambon is assistant foreign editor of "Channel 4 News". He is embedded with the US military in Iraq, in part of the Baghdad Security Plan