Leading article: Division, indecision and bad luck have all dogged US policy in Afghanistan

When the Prime Minister visited Afghanistan this month he returned with qualified optimism. He spoke of steady progress made in Helmand province and held out the possibility of British combat troops starting to scale back their presence as early as next year, with full withdrawal on track for 2015.

Across the Atlantic, President Barack Obama today publishes a review of US Afghan strategy which is reported to be in a similar vein. It cites "tactical gains" in Kandahar and Helmand, following the arrival of more troops and the application of more aggressive tactics since the autumn. In recent days, however, members of the US Congress have received official intelligence reports on both Afghanistan and Pakistan which paint a rather different, and bleaker, picture.

Pakistan's reluctance, or inability, to shut down militant sanctuaries in its tribal region, these reports say, means that Western forces can have only a limited chance of success. With the border essentially open, militants move freely from Pakistan, plant bombs, sabotage US troops, and flee back into Pakistan for refuge and new supplies. What this scenario implies, though this is not spelt out, is that the war in Afghanistan is interminable.

Now it is hardly unusual for military and intelligence assessments to be at odds. Intelligence services tend to look on the dark side, while the military – not just in the United States – are better known for optimism. Nor is it a bad thing for views to diverge. The President and his policymakers should have the benefit of as many informed judgements as possible. It is when heterogeneity ceases and one perspective is fixed that the biggest mistakes tend to happen – Iraq and its non-existent weapons providing a textbook example.

Such public rifts, however, contain dangers. In almost two years of office, Mr Obama has gained something of a reputation for "professorial" dithering. His initial review of policy towards Afghanistan dragged on for months before a – compromise – decision was taken; serious disagreements of principle periodically broke out into the open. This was not to the advantage either of Mr Obama's presidency or of the US position in Afghan-istan. Justly or not, it smacked of weakness.

But Mr Obama's problems have not all been of his own making. He has also been subject to a run of extremely bad luck. His then head of Central Command, General Petraeus, suffered a bout of ill health at the very time when Mr Obama most needed a strong presentation of his policies. Then, the US commander in the field at the time, General McChrystal, showed a quite startling lack of discretion in criticising his political masters, which brought his summary dismissal – just as his more sensitive approach to the safety of Afghan civilians seemed to be having a positive effect.

Now, with the sudden death of Richard Holbrooke, Mr Obama has lost his special envoy to Afghanistan and Pakistan and a key adviser. It can be said that Mr Holbrooke had been to an extent sidelined, as the military and the State Department came increasingly to the fore. With his particular combination of toughness and guile, and his track record of supremely difficult assignments, however, Mr Holbrooke is not easy to replace. And his chief merit was the same quality that made him unpopular in many circles: his bluff readiness to speak unpalatable truth to power.

In appointing Mr Holbrooke his special "Af-Pak" envoy, Mr Obama showed an early appreciation of the interconnectedness that makes anything approaching victory in Afghanistan so elusive. But after two years of almost constantly revised strategies and with Mr Holbrooke's accumulated wisdom now lost, Mr Obama's task looks as hard as it ever was.