As he leaves Iraq this week, the outgoing US commander, General David Petraeus, is sounding far less optimistic than the Republican presidential candidate, John McCain, about the American situation in Iraq. General Petraeus says that it remains “fragile”, recent security gains are “not irreversible” and “this is not the sort of struggle where you take a hill, plant the flag and go home to a victory parade… it’s not a war with a simple slogan.”

Compare this with Sarah Palin’s belief that “victory in Iraq is wholly in sight” and her criticism of Barack Obama for not using the word “victory”. The Republican contenders have made these claims of success for the “surge” – the American reinforcements sent last year – although they are demonstrably contradicted by the fact that the US has to keep more troops, some 138,000, in Iraq today than beforehand.

Playing down such killings, the Iraqi government and the US have launched a largely successful propaganda campaign to convince the world that “things are better” in Iraq and that life is returning to normal. One Iraqi journalist recorded his fury at watching newspapers around the world pick up a story that the world’s largest Ferris wheel was to be built in Baghdad, a city where there is usually only two hours of electricity a day.

The surge only achieved the degree of success it did because Iran, which played a central role in getting Nouri al-Maliki appointed Prime Minister in 2006, decided to back his government fully. It negotiated a ceasefire between the Iraqi government and the powerful movement of Muqtada al-Sadr in Basra, persuading the cleric to call his militiamen off the streets there, in March and again two months later in the Sadrist stronghold of Sadr City. It is very noticeable that in recent weeks the US has largely ceased its criticism of Iran. This is partly because of American preoccupation with Russia since the fighting began in Georgia in August, but it is also an implicit recognition that US security in Iraq is highly dependant on Iranian actions.

General Petraeus has had a measure of success in Iraq less because of his military skills than because he was one of the few American leaders to have some understanding of Iraqi politics. In January 2004, when he was commander of the 101st Airborne Division in Mosul, I asked him what was the most important piece of advice he could give to his successor. He said it was “not to align too closely with one ethnic group, political party, tribe, religious group or social element”. But today the US has no alternative but to support Mr Maliki and his Shia government, and to wink at the role of Iran in Iraq. If McCain supposes the US has won a military victory, and as president acts as if this were true, then he is laying the groundwork for a new war.