To the editor: Marines who served in Afghanistan are "frustrated," "angry" and "talking," according to your report from a city adjacent to Camp Pendleton. They have put their lives on the line and lost friends in an attempt to keep that nation out of the hands of the Taliban. This is the same frustration for many of those who fought beside me in the failed effort to keep Vietnam free from communism. What we need to realize is that there is no disgrace for us in defeat. We took an oath to the Constitution. Loyalty to that oath has helped preserve the right of Americans and others to life, liberty and the pursuit of happiness for more than 200 years. The outcome of events in Afghanistan may represent a defeat of the political objectives of four presidents. It is not, however, a defeat of the will of American men and women to put their lives on the line because they trust the value of the system to which they have sworn fidelity. The preservation of that system has always depended on loyalty to that oath, and it always will.