Rupert Cornwell: Obama must explain how he'll get them out

With his presidency at a critical juncture, Barack Obama tonight attempts to convince Americans that he has a credible strategy to wind down the US commitment in Afghanistan and gradually hand management of the war over to the government in Kabul.

In a long-awaited nationwide address from the West Point military academy, the President is expected to announce he is sending a further 30,000 or more American troops to fight in the eight-year-old conflict. Even more important, he must explain how this escalation of an increasingly unpopular war will help bring about a successful end – and indeed, how success in Afghanistan is defined. White House officials said Mr Obama would make clear that Afghanistan, where 68,000 US and 40,000 foreign troops are currently deployed, is not an open-ended venture, and that within a measurable timespan, most if not all of them would leave.

General Stanley McChrystal, the US commander in Afghanistan, told a visiting Congressional delegation last week that a drawdown of US troops could start by 2013, while Mr Obama's spokesman has said all US combat forces would be gone within "eight or nine years."

The President himself is unlikely to be so precise, but analysts say he must lay out a clear and convincing exit strategy. Mr Obama made his final decisions, and issued the first orders to implement them, at an unusual and unannounced meeting in the Oval Office on Sunday evening.

It was attended by Robert Gates, the Defense Secretary, General David Petraeus, who is head of US Central Command, and the President's National Security Adviser, General Jim Jones. Immediately afterwards, Mr Obama spoke by tele-conference with General McChrystal – whose August request for reinforcements of 40,000 personnel or more set in motion a painstaking policy review.

He also spoke with with Karl Eikenberry, the US ambassador in Kabul, who at one point was advising against sending any further US troops until Hamid Karzai's Afghan government clamps down on corruption in its ranks. And yesterday Mr Obama was contacting leaders of key US allies, including Gordon Brown, the French President Nicholas Sarkozy, and Italy's Prime Minister Silvio Berlusconi, to round up commitments for the minimum of 5,000 more soldiers Washington is trying to squeeze out of its NATO partners – some of whom face a domestic public opinion even more hostile to the war than in the US.

Afghanistan however is only one facet of a critical December for Mr Obama. The coming weeks will test to the limit his ability to keep Democrats united, ahead of next year's mid-term elections that already promise to be difficult for his party.

Yesterday the Senate started a make-or-break debate on healthcare reform. Democratic divisions mean it is far from certain that Harry Reid, the Democratic majority leader, will be able to round up the 60 votes needed to end debate and proceed to a final vote. If he fails, the measure could be doomed. At the same time Mr Obama is under growing fire over his economic management. Not only is unemployment if anything worsening, despite unprecedented budget deficits, but his efforts to rescue homeowners facing foreclosure are also foundering.

Even some normally sympathetic commentators are turning against him, accusing Mr Obama of either being too ruthless, or not tough enough. Though his personal popularity remains relatively high, his job approval rating has slipped below 50 per cent in some polls.

No test will be more critical than Afghanistan. Although Republican leaders generally support the force increase, many key Democrats do not – and Mr Gates and Hillary Clinton, the Secretary of State, are sure of a grilling when they testify on Mr Obama's new policy before key House and Senate committees on Wednesday and Thursday.

At the same time, vital parts of the Afghanistan equation are simply beyond Washington's control. Whatever performance benchmarks are laid down, there is no guarantee that President Karzai will be able to meet them. Officials talk about training an Afghan force of 400,000 to assume control of their country. But that process could be even more difficult than in Iraq. No less critical is the role of Pakistan. But the government of President Asif Ali Zardari is weak, even by Pakistani standards.

As a senior US official told The Washington Post yesterday: "Without Pakistan we cannot succeed."