The latest outbreak of fighting in Basra and in Baghdad's Sadr City is therefore bad news for McCain, and even worse news for the long-suffering Iraqi people who have been heartened by the sharp reduction in violence over the past year. In August last year, a survey of Iraqis found 60 percent of Iraqis saying their lives were bad against 39 percent who said they were good. Last month, the same survey found 54 percent saying their lives were good. And only 45 percent bad.

But the improved situation in Iraq was never simply about the 30,000 extra U.S. troops and the intelligent new strategies and training introduced by the counter-insurgency expert, General David Petraeus.

There were other crucial actors, all of them local. First was the Sahwa, "the awakening" of Sunnis in Anbar province rebelling against the al-Qaida zealots in their midst, and accepting American arms and training. Second was the ceasefire declared by the Shiite cleric Moqtada Sadr, nominal leader of the militia known as the Mahdi Army. Third was the steadily growing number of Iraqi troops and police, of widely varying quality, but at least giving an appearance of a security presence. Fourth was the rise in the oil price, which reminded Iraqis of all stripes that there was a highly promising future ahead for the country if only they could work out a stable way to govern themselves and divide the spoils.

This week's decision by the government of Prime Minister Nouri al-Maliki to demand that the Mahdi Army lay down their arms puts much of this at risk, even though the elected central government had to assert its authority at some point. There has been heavy fighting across the south and in parts of Baghdad, one of the main oil export pipelines has been blown up and the Iraqi government forces have found themselves outgunned by the Mahdi Army.

Sadr's motives and his objectives, like the degree of his authority over his militia, remain mysterious. But many observers see him as more of an Iraqi nationalist than Abdel Aziz al-Hakim, leader of the rival Badr Brigades militia and of the more pro-Iranian Supreme Council. Hakim is in the Maliki government coalition and Sadr is not, and so the U.S. forces who appear to be backing the fighting against the Mahdi Army are thus in the odd position of helping Iran's allies.

These complexities, and the surge in violence they have brought, should be an awful warning to McCain and other Americans of how little they know of Iraq, and of the power of complex internal Iraqi dynamics to affect the American election.