Physicist Steven Weinberg reviews the history of missile defense and argues that little has changed in the debate over the last 50 years. He concludes that "seeking to deploy a national missile defense aimed at an implausible threat, a defense that would have dubious effectiveness against even that threat, and that on balance would harm our security more than it helps it, the Bush administration seems to be pursuing a pure rather than applied missile defense—a missile defense that is undertaken for its own sake, rather than for any application it may have in defending our country."