When I visited Camp Bastion in Helmand province last year, I was stunned by what I saw. They have built what amounts to a small town from scratch in the desert, with some of the finest military hospital facilities in the world. They transport, maintain and repair a vast array of equipment in the searing summer heat and bitter winter cold. And the young men and women who are fighting the Taleban in our name do so with unswerving determination. It is difficult not to be swept up by the sheer heroism of the mission.

It was only when I left Helmand that the nagging questions began. Why, despite this heroic effort, are we still no nearer to victory? The answer is brutal — the political strategy required for success has been missing for the eight long years we have been in Afghanistan.

I have always supported the aims of the mission, but I find it morally reprehensible to ask young men and women to risk life and limb in conflict without a strategy. That is why six months ago I felt it was finally time to break the political consensus on this war and start asking publicly the difficult questions. Predictably enough, I was accused of looking for a way to drop the Liberal Democrat commitment to our mission. Yet I believe it is the duty of politicians to ask why soldiers are dying in pursuit of a strategy that isn’t working.

The question now is whether a new strategy can turn things around. That is why all eyes are on President Obama. His long-awaited announcement of a new approach will be pivotal in determining whether the international community can still succeed. So far, attention has focused on whether he will commit more troops, as requested by General Stanley McChrystal, the commander of Nato forces in Afghanistan. Certainly, extra troops are a necessary component of success, but, as General McChrystal acknowledges, far from sufficient. It would be senseless to send more soldiers to Afghanistan if the underlying strategy is not changed to give them a meaningful chance of success.

Afghanistan is a complex, tribal society that has been on the receiving end of invasion and counter-invasion for generations. The Taleban control huge areas of the country, warlords are powerful and tribal divisions run deep. Corruption is endemic. Opium production is one of the few ways to make a decent living, and drug addiction is on the rise, even among the fledgeling national police force. Mr Obama must set the bar extremely high if he is to succeed and the rest of the coalition is to follow him. To do that, his strategy must incorporate immediate and dramatic change in four areas.

First, we have to deal with the crisis of legitimacy of the Karzai Government. Hamid Karzai has promised to reach out, but has not yet gone anywhere near far enough. If he were to convene a Loya Jirga to disperse power to tribal leaders, as well as bringing in rivals and tackling corruption in the Government in Kabul, that would show immediate good faith. Otherwise, international governments will have no choice but to bypass him, in particular on aid and reconstruction.

Second, the new approach must encompass the countries that border Afghanistan. The big powers in the area — Russia, China and Iran — all have an interest in seeing a stable Afghanistan, and must be involved in efforts to secure peace. Third, we need a shift in the military strategy, to focus on population centres where we can win hearts and minds, rather than trying to defend remote desert outposts. And finally, we need to engage and negotiate with non-core elements of the Taleban. A properly funded reconciliation plan must be rolled out to encourage Taleban fighters to switch sides.

Each of these elements must be taken into account in Mr Obama’s strategy if it is to provide the step-change necessary to turn the conflict around.

But even if this new strategy makes sense on paper, there is no guarantee it will succeed. If it does, I believe British combat troops will be home well within the next Parliament. That is what I believe the vast majority of British people want — our troops back home having succeeded, not failed. That is also why we must be much more vigilant in scrutinising any new approach. Given the length of time it takes to deploy new troops, it is unlikely that we will see significant change in the military dynamic until well into next year, but we should be able to tell whether the political changes are making headway much sooner.

The final ingredient of success in Afghanistan is political leadership here at home. We need relentless explanation from the Government about why this war is necessary. The inability of both Tony Blair and Gordon Brown to explain the Afghan conflict is one of the most shocking failures of political leadership in recent times. People need to understand that the knock-on effects of a Taleban-run Afghanistan could be catastrophic, potentially tipping Pakistan, a nuclear power, towards civil war. Defeat could destroy the legitimacy of Nato and would be a huge boost to the Taleban and al-Qaeda, ultimately making British people less safe.

That is why I hope that a new, successful strategy can still be deployed. There are many people who are beginning to believe withdrawal is the only option. If we fail to adopt a new approach, it inevitably will be. But I believe we owe it to the men and women who have already died in this conflict, and to the hopes of greater stability in the region and the world, to finally get this right. President Obama’s announcement represents our last chance of success. If he delivers the plan we have long argued for, it will deserve our support. If he doesn’t, I would struggle to look British voters in the eye and say that we should carry on with this war.

Nick Clegg is leader of the Liberal Democrats

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