By Adam Brookes
BBC News, Washington
President Obama outlined his strategy after months of deliberation
America and Nato will tough it out in Afghanistan for another 18 months. And then things will start to change.
That was the central message of President Obama's speech to the nation on Tuesday night, in which he outlined his new strategy for Afghanistan.
For those 18 months, the strategy provides a reinforced American and Nato presence to tackle the Taliban and to secure the country's key population centres, allowing the Afghan government and armed forces breathing space.
It is a window of opportunity for Afghanistan, and for the government of Hamid Karzai. And, Mr Obama seemed to suggest, this would be President Karzai's final opportunity to demonstrate leadership while still enjoying the full weight of American military backing.
Because in July 2011, the president said, the US and Nato would start handing areas of the country back to the control of Afghan security forces - allowing the drawdown of foreign troops to begin.
So President Obama has signalled to Afghanistan that America is reinforcing and staying in the fight - but the commitment is "not open-ended".
And he has signalled to war-weary Americans that a process is underway that should allow the troops to start coming home - perhaps more quickly than many had thought likely.
The 30,000 additional US troops will deploy to Afghanistan over the next six months. They will be combat soldiers, but many thousands of trainers, too, who will work on expanding the Afghan army and police - the key task facing the US and Nato.
The combat troops will deploy into Helmand and Kandahar provinces, and into the east of the country, all areas where Taliban influence has spread.
In total, 100,000 American troops will be in Afghanistan by the end of the summer. That is a deployment that has become comparable in scale to that in Iraq.
And what of their objectives?
The primary aim of the deployment, said the president, is to disrupt, dismantle and defeat al-Qaeda, and prevent its return to Afghanistan. That is a long-standing war aim. And still unexplained is how al-Qaeda in Pakistan will be dismantled.
"We must reverse the Taliban's momentum and deny it the ability to overthrow the government," said the president. Not defeat them, you will notice.
Look for efforts to bring tribal or village militias into patrolling their locale, guarding strategic locations and resisting the Taliban's influence. Again, echoes of Iraq
A senior administration official spoke of "degrading" the Taliban. A "degraded Taliban", according to the official, is one which is unable to return to power, or take Kabul by force.
There seems to be an acknowledgement here that a level of insurgent activity will continue in Afghanistan - even in the best case scenario. Wiping out the Taliban is not a war aim. And given the Taliban's ability to make use of parts of Pakistan as a safe haven, nor could it be.
Under the strategy, reinforced Nato and US units will secure key population centres - the big cities and towns. This is meant to give the Afghans time to get their own army and government on their feet. This sounds very similar to the stated aim of the surge into Iraq in 2007.
The July 2011 date requires that, by then, elements of the Afghan armed forces are in sufficiently good shape to begin taking on sole responsibility for security. The first areas of the country handed over would be those that are quietest and least vulnerable to Taliban influence.
This is a very rapid timetable - accelerated, the president called it - and there will be many in the US military who wonder if it is optimistic, given the difficulties of finding competent leaders for the Afghan army and police.
And the message for President Hamid Karzai was clear: shape up, and soon.
"This effort must be based on performance. The days of providing a blank cheque are over. President Karzai's inauguration speech sent the right message about moving in a new direction. And going forward, we will be clear about what we expect from those who receive our assistance," the president said, ominously.
There may be more efforts to engage Afghan villagers and militias
A senior administration official today spoke of the importance of working to improve governance in Afghanistan, but doing so "from the bottom up".
Implicit in those comments was the sense that the central government of Hamid Karzai is ineffectual in most of the country. This "bottom up dynamic", as one senior administration strangely put it, means the US will be looking for local solutions - perhaps accommodations with tribal leaders or local strongmen to enhance local security.
The senior administration official said Nato was already experimenting with ways to "link traditional structures" into the security structures of the state.
So look for efforts to bring tribal or village militias into patrolling their locale, guarding strategic locations and resisting the Taliban's influence. Again, echoes of Iraq.
And look for efforts to strip away from the Taliban cause elements who are less radicalised, and more amenable to deal making.
The civilian effort in Afghanistan - reconstruction, aid, development - will be enhanced, too, and refocused, according to the president. Non-corrupt organisations and ministries will get the development money.
And the remaking of the agricultural sector, as something that has a rapid and direct effect on ordinary Afghans, will be a top priority.
Some of the president's key advisers will testify before Congress this week
But Washington experts on post-conflict reconstruction still worry about the civilian part of the puzzle.
"There are so many moving parts here," says Karin von Hippel at the Center for Strategic and International Studies. "The aid agencies, the Afghan government, the US state department, USAID: until they're aligned - and they're not - the military can be successful but the civilian success won't necessarily follow."
"We need a strategy that works on both sides of the border," said Mr Obama. He pledged to support Pakistan in politics, its economy and its security "long after the guns have fallen silent".
But he warned that "we cannot tolerate a safe-haven for terrorists whose location is known, and whose intentions are clear".
The new strategy, said the administration official, will aim to keep the Pakistanis focused on the pursuit of al-Qaeda, and to sustain their fragile democracy. There were very few specifics here, but a resounding acknowledgement of Pakistan's centrality to the entire security equation.
In the end, though, this was a speech aimed primarily at Americans, in the hope that a new sense of urgency and purpose will permeate the entire Afghan effort and shore up public support for the war.
Mr Obama was speaking particularly to those members of his own party in Congress, including those who are doubtful that America can achieve any of its stated objectives in Afghanistan, and can ill afford the blood and treasure it will take to try.
On Wednesday, US Defence Secretary Robert Gates, Secretary of State Hillary Clinton and the Chairman of the Joint Chiefs of Staff, Admiral Mike Mullen, are due to testify before Congress on Capitol Hill.
Those hearings will tell us much about the degree to which the heavyweights of the Democratic Party - House Speaker Nancy Pelosi, Senators John Kerry and Carl Levin - are fully behind the president in his attempt to rejuvenate the military effort in Afghanistan.