Reading Andrew Coyne's piece on North Korea and the need for Canada to join the American Ballistic Missile Defence System reminded me of lots of old deterrence theory stuff. The piece raises good questions about the reliability of the key actors, especially Trump, but confuses what is necessary for deterrence. Still, there are some problems that we need to think about.
The big problem in the piece is that Coyne thinks that the American commitment to defend its East Asia allies is now largely unbelievable with the North Koreans developing the ability to strike the continental US (and Canada). It is true that the US, under several Presidents, has failed to deter the North Korean effort to develop both nuclear weapons and the missiles to deliver them. But deterring their effort to develop some deterrence and deterring an attack on allies are two different things. Coyne is right to point out that extended deterrence (don't attack my allies or else) is less believable than regular, vanilla deterrence (don't attack me or else). The threat to start or expand a nuclear war is problematic in either case, but seems a bit more believable if it is in retaliation for a big attack on the homeland.
The key is that for deterrence to work, the side being deterred (North Korea in this case for the moment) does not need to be certain that a counter-strike would happen. They just need to think that there is some possibility of such a response. Why? Because the costs of nuclear war are so very high, if one does the probability math (probability of x times value of x), the prospective costs of attacking first are simply too high compared to the status quo (.01 times infinity = infinity) .... as long as the status quo is bearable (which is why we have to stop threatening regime change). We do not have to convince North Korea that a retaliatory strike is certain if North Korea attacks South Korea and/or Japan, but that it could happen. The placement of US troops in South Korea is far more about being a tripwire to raise the probability of the US responding than actually defending South Korea in a conventional attack.
Again, one might say that this is not sufficient, but the key to nuclear threats is that classic Schelling phrase: a threat that leaves something to chance. One does not have to threaten, for instance, total nuclear annihilation of North Korea crosses the Demilitarized Zone--one just has to threat to start a process that might lead to things getting out of hand and ultimately leading to nuclear war. This was the old extended deterrence logic for Europe and Asia during the cold war.
Certainty? That is for allies. That is, the tripwires and all the rest over the years are mostly aimed at reassuring allies. The enemy is deterred by a modest chance of the US responding, of sacrificing Chicago for Bonn or now Seattle for Seoul. The allies? They are very nervous and require a great deal of assurance. Ballistic missile defense both in the region and in the US might assure them somewhat--that the US can stick around and meet its commitments knowing that it is protected.
Except for one thing: BMD may be at best a coin flip. We have lots of uncertainty about whether the efforts to invest in destroying missiles in flight have produced anything remotely reliable. Again, that is ok from a deterrence perspective--uncertainty is not bad.
While I think that joining the US BMD program makes sense, my reasons do not center on the NK nuclear threat. The US would try to stop an attack on Vancouver or Toronto since they are very close to American cities whether Canada is in or out of the BMD program. And North Korea is not going to be gunning for Calgary or Edmonton. North Korea barely notices Canada, and, given its small supply of nuclear arms, it will not be aiming at Canada. The BMD arguments I buy have more to do with building a robust NORAD that addresses a variety of threats in the 21st century, and strengthening a key US-Canadian institution in these uncertain times.
While we should all doubt Donald Trump, I am far more worried about his starting a process that leaves something to chance via a small strike at North Korea's missiles or at its leadership than I am about his not responding to a North Korean attack. Yes, we are now deterred from attacking North Korea, but that has been true since it developed the capability level Seoul with its artillery. Yes, we have much to worry about, but then so does Kim Jong Un. If he wants to survive, he will avoid a process that might lead to escalation. The costs of being wrong are just too high.