This paper analyzes what might be expected to happen if a 10-kiloton nuclear bomb exploded in a U.S. city; the example used for this analysis is San Francisco. The analysis draws from research projects the author has done in recent years for the Department of Homeland Security and other government organizations, including observing and providing critique on TOPOFF 2 (Top Officials), an exercise of federal, state, and local emergency response systems to terrorist attacks. The paper summarizes a number of talks the author has given to students and professionals working on security issues.