President Barack Obama’s announcement this week that he will delay the withdrawal of some 4,000 U.S. troops from Afghanistan is an acceptable course correction. Keeping troop levels at their current strength will allow the United States to continue training Afghan forces while also helping with counter-terrorism efforts, officials said. If those efforts help stabilize the country and prepare it for the moment when the U.S. withdraws for good, that’s fine with us.

The bigger question is what the United States will do at the end of 2016, when Obama has promised a “final consolidation” that will shrink the U.S. presence to fewer than 1,000 troops stationed at the U.S. Embassy in Kabul. That deadline has always seemed more political than strategic, and it is not fully clear why the president and his advisors think the Afghans will be ready even then to assume management of their own conflict. We’d like to hear more from Obama about how he intends to ensure that the U.S. is not involved in Afghanistan in perpetuity — and at the same time ensure that the country doesn’t disintegrate into warring factions or revert to Taliban control when the Americans leave.

This week’s decision to delay the withdrawal, announced during a visit to Washington by Afghan President Ashraf Ghani, means that the U.S. military presence will remain at 9,800 through the end of this year, compared with a force that once numbered 100,000. Since last year, the U.S. role has been confined to counter-terrorism operations and training Afghan forces. The assumption of combat responsibilities by Afghan forces is reflected in the decline in U.S. fatalities: only 55 in 2014 and none this year.

But clearly there is a concern that the Afghans are not yet prepared to wean themselves off American support and fight their battles alone. Obama said he was delaying the promised withdrawal in order “to help Afghan forces succeed so ... we don’t have to respond in an emergency because terrorist activities are being launched from Afghanistan.”

It’s certainly conceivable that, with further training of Afghan troops, additional U.S. military assistance and the help of President Ghani, Obama’s 2016 withdrawal date will be feasible. But it’s also possible that the Taliban will have gained ground and that Islamic State, which Obama has vowed to “degrade, and ultimately destroy,” will have established a significant presence in Afghanistan.

What then? If that were to happen, it’s all too easy to imagine the Afghan government pleading for another deferral. On what grounds would Obama say no? He could hardly cite his desire to secure his political legacy before he left office.

We have supported Obama’s effort to extricate the U.S. from protracted and costly wars in the Middle East. But it is hard not to be reminded of what happened in Iraq, where U.S.-trained local forces collapsed in the years after the Americans withdrew. In Afghanistan, Obama should offer more than assurances; he should explain how this is going to work.