Gordon Brown is right today to be setting out – and he should keep setting out – the basic case for Britain’s involvement in Afghanistan.

As Paddy Ashdown said yesterday, this war will not be won or lost militarily, but in the bars, sitting rooms and workplaces of those countries – democracies – who are contributing the soldiers putting their lives at risk.

So the democracies have to be persuaded, again and again, that the sacrifice and bloodshed is worthy of the cause. Not easy against the backdrop of a corrupt and widely discredited Afghan leadership being re-elected. Nor when we know so much of the drugs on our streets comes from there. Nor when an Afghan the British are training turns fire on them and adds to our war dead.

The current situation reminds me of an important moment during the Kosovo crisis when President Clinton and Tony Blair came to the view that however mightier, in military terms, Nato was against Milosevic’s forces, the public opinion battle was being lost, putting the entire strategy at risk.

What’s more, in some ways it was easier to explain Kosovo. Night after night TV was telling the stories of barbarism and butchery as people fled ethnic cleansing in their tens of thousands. Basic human sympathy was also matched by a hard-headed worry among leaders and public alike that today’s refugees would become tomorrow’s additional strain on EU countries like ours.

And even with those factors at play, it was hard enough.

Afghanistan is harder. The memories of 9/11 and 7/7, for many, are not as powerful as they were. The threat to troops on the ground is all too clear. The threat they are seeking to contain – terrorism fostered there then implemented here – is less clear, and when prevented it is invisible, so less easy to explain. The complicated politics of the region, Pakistan’s as well as Afghanistan’s, make it even harder.

But the other recollection I have from Kosovo is that when the explanation is clear, detailed, and co-ordinated across the countries involved, then the public will listen and understand, even when things go wrong.

As in so much else, the US have to take the lead. The decisions President Obama has in his pending tray are about as big as they get for a leader. That explains why he is taking his time.

As I said on a vlog here recently, I think Obama, facing a newly resurgent and pretty vicious Republican Party, is a good man doing a good job, and he deserves continuing support. But it is harder for Britain, and the other countries involved in Afghanistan, properly to explain the situation without the absolute clarity of strategy from the US.

As well as giving leaders space to explain, the public will also give leaders time to reach difficult decisions. But the US strategy needs that real clarity pretty soon. Then, as the military strategy unfolds, there has to be a concerted and internationalised communications strategy alongside it.

Nato v Milosevic, militarily, was like Manchester United against a Conference team. It is the same now, though the Taliban are in some ways an even tougher opponent than the Serbs back then.

But Ashdown is right that public opinion, in the collection of democracies involved, is where the strategy can be derailed.

So GB is right to be out there today, explaining. But it will become a lot easier for him and the other leaders involved when Obama has spoken clearly and definitively on the medium and the long term, and how the objectives for both are to be met.