To increase the odds for a more manageable transition and avert an economic collapse, the United States and other major donors have pledged $16 billion in economic aid through 2015. That is a commitment worth keeping, but the United States and its allies have tried nation building in Afghanistan, at least for the last four years. It is not working.

*

The task is to pack up without leaving behind arms that terrorists want and cannot easily find elsewhere (like Stinger missiles) or high-tech equipment (like Predator drones) that can be reverse engineered by Pakistan or other potential foes. The military can blow those things up if it must.

It is hard to be exact about a timetable since the Pentagon and NATO refuse to discuss it. The secretary of defense, Leon Panetta, told us last week that decisions about the timetable would be made after the military command reported to Mr. Obama in December. He would not say much of anything beyond that — whether the withdrawal would be front-loaded, or back-loaded, or how many troops would be needed to secure the election.

Some experts say a secure withdrawal would take at least six months, and possibly a year. But one year is a huge improvement over two. It would be one less year of having soldiers die or come home with wounds that are terrifying, physically and mentally.

Suicides among veterans and those in active service reached unacceptable levels long ago. A recent article by The Associated Press quoted studies estimating that 45 percent of returning veterans from Iraq and Afghanistan are claiming disability benefits. A quarter of those veterans — 300,000 to 400,000, depending on the study — say they suffer from some form of post-traumatic stress disorder. This is far too high a price to go on asking of troops and their families.

Four years ago, Mr. Obama called Afghanistan a “war we have to win.” His strategy relied on a newly trained Afghan Army and police force that could take over fighting the Taliban; a government competent to deliver basic services; and Pakistan’s cooperation. Here is what happened:

AFGHAN SECURITY FORCES NATO and the Pentagon built an Afghan Army and police force of nearly 352,000 that is now nominally in the lead for providing security in most of the country. Attrition rates are high and morale is low; the attacks on coalition forces have eroded trust and slowed the training. Afghan leaders have to work harder with Washington to weed out corrupt troops and Taliban infiltrators, but the nation cannot hang its hopes on that happening.

There is an agreement to finance the army to 2017 with Kabul paying $500 million, Washington about $2.5 billion and other donors about $1.3 billion. If Kabul keeps its commitments, the donors should make good on theirs.