The parallels with the invention and first use of atomic bombs on Hiroshima and Nagasaki are eerie. Consider the similarities: First, government and scientific leaders invent a new kind of weapon out of fear that others will develop it first and threaten the United States. Second, the consequences of using the new weapon — both the material damage it might cause as well as its effects on international security and arms-race dynamics — are poorly understood. Third, scientists and engineers warn political and military leaders about the dangers of the new weapon and call for international cooperation to create rules of the road. Fourth, despite warnings by experts, the U.S. government continues to develop this new class of weaponry, ultimately unleashing it without warning and without public discussion of its implications for peace and security.