Thank you to Bill, Mike, and Matt for an interesting and enlightening discussion of my new book, On Nuclear Terrorism, over the last week. In their final posts, Matt and Bill lay out a set of points where we all agree. I concur. In the spirit of debate, though, I’ll part with some lingering worries that this discussion reinforces for me.

I remain concerned that people who think about nuclear terrorism are unjustifiably wary of learning from what people who think about terrorism more broadly have found, especially when it comes to how terrorist groups behave. (Read: aversion to failure, conservative approach to operations.) To me this is one type of worst case thinking at work. In the worst case, a terrorist group will exploit every hole one can imagine. In reality, it won’t. That leads to different assessments of the effectiveness of various defenses. If we ignore findings about how groups make decisions, we’re going to miss important opportunities.

This is closely related to another worry of mine that persists. One of the central points flowing through my book is that we need to ask, when looking at options, whether they can improve our defense, not just whether they have failings. For example, I look at the well documented and widely (though, of course, not universally) agreed finding amongst terrorism scholars that many if not most successful and ambitious terrorist groups are averse to failure and behave conservatively as an opportunity: it allows us to identify defensive tools that might be effective against some groups even if, and while, they are not as useful against others.

The opposite pattern – focusing on the situations in which particular defensive tools may fail, rather than also on looking for opportunities to employ them effectively – has shown up frequently in this week’s discussion. There is an odd contrast between this approach and that used when talking about security for nuclear weapons and materials. There, we applaud rudimentary upgrades, even while rightly chiding officials to do more. But when it comes to the rest of the defense, we too often seem to skip the applause (or at least the constructive criticism) and move straight to finding holes. Had that attitude applied when materials and weapons security programs started up in the early 1990s, those would never have gotten off the ground.

Let me made a final point on the theme of finding opportunities, not just failings, in broader defenses. When experts on nuclear terrorism talk about broader defenses, they usually focus on things like radiation detectors. But many of the real opportunities are in areas, like law enforcement and intelligence, that are not “nuclear” in any traditional sense. Investments in those areas could address more likely threats while also confronting the nuclear possibility. They deserve special attention as a result.

Bill opens another thread, and I can’t help but weigh in, because it’s an important one. He asks about how politics, domestic and international, complicates efforts to secure nuclear weapons and materials. (I’d add, as readers should expect by now, that we should also be thinking about how those same dynamics complicate efforts to strengthen the rest of our defenses.) He’s right to identify this as a missing part of this week’s discussion. I’m inclined to think that U.S. nuclear dominance doesn’t play a big role (which is not to say that it does not have other effects on international dynamics) but that other points of friction certainly do. A resurgent Russia doesn’t feel like it needs American assistance, and U.S. policies need to be crafted in a way that is sensitive to that. I’ll also flag one bit of recently popular policy thinking that I think would make things immeasurably worse (and that I address in the book). Some have proposed that the United States threaten retaliation against states (including Russia) that inadequately secure nuclear materials that are later used in terrorist attacks. While superficially appealing, that sort of threat would probably be deathly for efforts to cooperatively secure loose nukes.

Again, thanks to all, including to those who have posted comments – it's been an interesting discussion.