(The Washington post): Jarrett Blanc is a senior fellow in the Geoeconomics and Strategy Program at the Carnegie Endowment for International Peace. He was the deputy special representative for Afghanistan and Pakistan from 2012 to 2014, responsible for U.S.-Taliban negotiations, and was principal deputy special representative for Afghanistan and Pakistan from 2014 to 2015.The United States has spent years slowly losing the war in Afghanistan. We have recently been losing with about 14,000 troops, but we were slowly losing in 2010 with 100,000 troops as well.We are not losing because of tactics or troop numbers but because of a catastrophic failure to define realistic war goals. After a messy but basically successful counterterrorism effort, we expanded our objectives in ways that were bound to fail. We mortgaged our counterterrorism objectives to more maximalist aims, making our original ambition harder to secure.U.S. security requirements and national interests cannot begin to justify the human, strategic and financial costs of a continued, large-scale U.S. military presence in Afghanistan. It is long past time to accept the risks and difficult compromises of a negotiated settlement; they only become more severe the longer we delay.Afghanistan’s civil war is now entering its third generation. America’s war in Afghanistan is entering its second, but the United States and the Taliban are reportedly close to agreeing on a framework for resolving at least the U.S.-Taliban war. The deal’s central elements reflect the core aims of the two sides: The Taliban gets a U.S. commitment to withdraw, and the United States gets a Taliban commitment to police the territory it controls against internationally focused terrorist groups.Critics argue that Washington should have held off on these issues until the Afghan government reached an agreement with the Taliban about the future of Afghanistan. That argument appeals, but it was tried and repeatedly failed. The Obama administration hamstrung its diplomacy by refusing to compromise on this preferred sequence.An initial agreement to address core security issues does not, however, mean that all U.S. interests have been addressed or all U.S. leverage expended. Washington needs to try to shape a settlement that ends the worst of the civil war and protects a kind of stable social and political decentralization that reflects the actual powers of the parties.