Americans have often been accused of having short attention spans but this seems particularly unsettling.

A useful corrective was offered last week by Ryan Crocker, who retired from the US foreign service earlier this year after a 37-year career that was capped by his stint as ambassador in Baghdad at the time of the surge.

Speaking at the Harvard Kennedy School on Friday he told a large crowd not to kid themselves that America's adventure in Iraq is all but over. "It's still just getting under way," he said. "Huge challenges that neither we nor they can identify, will emerge in the future."

Noting that America had engaged in a long, and very public, discussion over whether to go into Iraq, he called for an equally spirited discussion about when and how they intend to leave.

The problem is that far too many people — both within and outside the political world — are avoiding this conversation. They do so because they assume, incorrectly, that the issue is more or less settled.

Shortly after last year's American presidential election, the US and Iraq finalised a Status of Forces Agreement (Sofa) to replace the UN mandate under which American troops in Iraq had operated since 2003. Under the terms of this agreement, US forces spent much of the spring and summer pulling out of Iraqi cities as a first step toward leaving the country entirely by the end of 2011.

Like any international agreement the Sofa can be modified if, at some point in the future, both governments agree there is a need to do so. It is rarely said in Washington, but widely assumed, that this means the actual implementation of the withdrawal agreement is essentially situational: that is, it will go ahead only if conditions on the ground warrant it.

Despite the fact that Iraqi Prime Minister Nouri Al Maliki has emerged as a stronger, and far more savvy, political player than almost anyone expected; and despite the fact that the existing Sofa was only grudgingly approved by the Iraqi parliament, there remains a near universal assumption in Washington that if, come 2011, Washington decides we need to stay longer, then so be it. Last May, the army chief of staff, General George Casey, acknowledged as much, telling a group of journalists and think tank specialists that his planning scenarios envision the presence of US combat troops in Iraq for another decade.

Finally, and perhaps most importantly, there has been little discussion here in the United States about what ‘withdrawal' really means. As Crocker emphasised last week at Harvard, the US policy has always been that it wants no permanent bases in Iraq. Crocker, however, failed to note that government officials and the general public often have starkly different definitions of "permanent base."

The official view of these things tends to be legalistic. Washington has maintained significant bases in Qatar since the mid-90s, in Kuwait since 1991, and in Bahrain since 1971. The Americans lease these bases from the host governments. Since those leases have expiration dates (that is, they need to be renegotiated every so often) the bases in question are not, technically speaking, "permanent".

Ordinary citizens of both the US and the host countries could, however, be forgiven for concluding that any base that has been in place for nearly 20 — let alone 40 — years and shows no sign of going anywhere is, to all intents and purposes, permanent.

Beyond that there is the question of what ‘withdrawal' actually means. The military tends to make a distinction between training or advisory troops and combat forces. The American approach to Iraq raises the very real possibility of combat forces heading home while tens of thousands of trainers, advisers and their accompanying support troops remain in place. A military professional might call such a situation ‘withdrawal', but a lot of ordinary Americans and Iraqis are likely to think otherwise.

America seems to have a collective attention span capable of taking in only one war at a time. For years we were so focused on Iraq that many people seemed to forget that Afghanistan remained unresolved. Now, when Afghanistan is a daily topic of conversation in the US, Iraq has become the forgotten conflict.

It is time, as Ambassador Crocker says, for a more public, more focused, discussion about what ‘getting out' of Iraq really means. Americans and Iraqis alike may well be unhappy with what they hear.

 Gordon Robison, a writer and commentator who has lived in and reported on the Middle East for two decades, teaches political science at the University of Vermont.