inherited. The war devastated Johnson's domestic efforts. Obama faces the same threat. Both wars have been justified as wars of necessity. With Vietnam, proponents warned that the fall of Southeast Asia to communism would vastly strengthen the Soviet Union and China. In an era when American schoolchildren were being taught to duck and cover under their desks in case of nuclear war, this warning about Vietnam also made the war seem essential. Today, the necessity stems from the claim that failure would resurrect the dangers we faced before 9/11. And both presidents escalated wars where the path to victory and the potential costs -- in terms of human capital and budgetary obligations -- were unclear. Despite the fact that Johnson confronted a very different kind of enemy, the risk today is enormously high. In Afghanistan, the U.S. is dealing with a war front that is notoriously treacherous, as the Soviets learned in the 1980s and the U.S. has learned since 2001. The U.S. is also depending on a highly corrupt and undependable government in Afghanistan. While the promise of withdrawal in July 2011 might be accurate, presidential assurances of benchmarks and end games historically do n't come true. The one constant in warfare is that it is unpredictable and difficult to control. One day after Obama's speech, Defense Secretary Robert Gates indicated that the deadline was not