Image Taliban fighters in the Alingar district of Laghman, Afghanistan, last year. Credit...Jim Huylebroek for The New York Times To the Editor: William Ruger’s argument for a precipitous withdrawal of U.S. troops from Afghanistan works only if we forget what we’ve learned and pretend that there will be no consequences for us and our Afghan partners. A year ago, the Taliban promised the United States that it would prevent terror groups from regrouping in Afghanistan, pursue peace with the Afghan government and others, and contribute to a more stable and secure country. But the Taliban is failing to deliver on all of these, and other, promises.