OF THE multiple foreign policy problems inherited by President Biden, that with the shortest fuse may be Afghanistan. A deal struck a year ago between the Trump administration and Taliban insurgents called for the United States to gradually withdraw its forces over a period of 16 months, in exchange for commitments by the Taliban to break ties with al-Qaeda, reduce the level of violence and open negotiations with the Afghan government. The Taliban, according to U.S. and international officials, didn’t keep its promises — especially that of severing relations with al-Qaeda — but President Donald Trump nevertheless pushed down the level of U.S. forces from 14,000 a year ago to 2,500 when he left office.

The Biden administration now has mere weeks to decide whether to follow through on the withdrawal of the remaining American forces and contractors by May 1, as the deal provides. U.S. allies, who have 8,000 of their own troops still in the country, will want to know Washington’s intentions by the time of a NATO meeting on Afghanistan later this month. Last week, a study group established by Congress recommended that Mr. Biden launch a diplomatic push to win acceptance of a delay in the final withdrawal so as “to give the peace process sufficient time to produce an acceptable result.” While that course has distinct risks, it is better than the alternatives.

The most likely consequence of a full U.S. and NATO withdrawal by May, the study group concluded, would be the resumption of full-scale civil war among the Taliban, the Afghan government and other factions. That would open the door to al-Qaeda, the Islamic State and other terrorists. U.S. withdrawal, said study group co-chair retired Gen. Joseph F. Dunford Jr., a former commander in Afghanistan and chairman of the Joint Chiefs of Staff, would make the country a base for terrorism again within 18 to 36 months. All the other gains the United States has fought for over nearly 20 years in the country, including rights for women, a vibrant civil society and the rudiments of democracy, could also be lost.

The alternative is not to reembrace a military strategy of defeating the Taliban; it is clear that war cannot now be won. But “further U.S. troops withdrawals,” the study group report says, “should be conditioned on the Taliban’s demonstrated willingness and capacity to contain terrorist groups, on a reduction in the Taliban’s violence against the Afghan people, and on real progress toward a compromise political settlement.”

The study group suggests that Afghanistan’s neighbors, including Pakistan, Russia, India and perhaps Iran, could be enlisted to pressure the Taliban to accept an extension of the May 1 deadline; those nations have a common interest in Afghanistan not becoming a sinkhole of terrorism. Without such a deal, a delayed withdrawal could cause the Taliban to resume attacks on U.S. forces, which it has stopped in the past year. It’s possible, too, that more troops would be needed to prevent a collapse of government forces, which have been under mounting pressure from the insurgents.

Those difficult steps are nevertheless preferable to abandoning Afghanistan. The United States, said the report, “is prepared to withdraw from Afghanistan. It should not, however, simply hand a victory to the Taliban.”

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