The MoD response has been instructive, and given a foretaste of how difficult this matter could be in 2015, around the time of the next election. "UK forces will no longer be in a combat role or in the present numbers by 2015 but may remain to train and mentor the Afghan forces after that," it begins — a statement that makes some sort of internal sense. But then it continues: "what we cannot do is to see a reduction in our combat troops until we are sure that we've got sufficient and lasting security." Which leaves a question hanging awkwardly in the air: will we have achieved "sufficient and lasting security" in Afghanistan by 2015? The answer, surely, is that we cannot tell.
This could leave Cameron open to either of two criticisms come election time, even more so than now. If our troops are withdrawn from an Afghanistan that is still mired in conflict and disarray, then he might be attacked for prematurity. If they are left in the country to preserve a "lasting security," then he might be attacked for going back on a promise. Timetables may look neat on paper, but there's always the prospect of entanglement and confusion further down the line. Anything other than a clean withdrawal from a stable country, and Labour will make play.