In Keir A Liebers' and Daryl G. Press' The Nukes We Need, they make an argument for the application and development of tactical nuclear weapons. Liber's & Press' argument rests on the position that using tactical nuclear weapons adds to the credibility of our nuclear arsenal, and thus increases the U.S.' power to deter aggressors. This argument is flawed in many ways.
First, they make the argument that in conventional wars against powerful U.S. adversaries, we will use nuclear weapons because of the existential threat. However, these authors ignore the fact that the deterrence we have already established has halted these great power wars. The U.S. and China have not fought, the U.S. and Russia have not fought, Russia and China have not fought and so on. Why do we need to develop tactical weapons, as a means to hit counterforce targets, if these wars do not begin in the first place?
Secondly, the use of tactical nukes will have the opposite effect of deterring aggressors and nuclear war. They will in fact increase nuclear wars because other states will believe we are more likely to use them. The very argument that Lieber and Press lay out in arguing for tactical nukes "that we would actually be more likely to use them" is the at the heart of the counter argument. The nuclear threshold will likely be lowered and we will see tactical nuclear weapons employed more often.
Third, and most troubling is their position that a tactical nuclear attack is vastly different from any past nuclear attack. Once the nuclear threshold is past, the nuclear threshold is past. Are powers likely to respond more benignly if we insist that we only dropped a tactical nuclear weapon on them? The enemy may not respond in kind and still deploy a devastating second strike. Finally, tactical nukes, while having left radioactive fallout, still have radioactive fallout. Thus, these weapons are more moral than larger nuclear weapons, but cannot claim complete moral superiority.
Finally, tactical nuclear weapons do not have capabilities that differ from conventional weapons the U.S. now possesses as much as they would lead you to believe. U.S. weaponry has become increasingly sophisticated, lethal and accurate. We can handle many of the potential dangers that Lieber and Press speak about without crossing the nuclear threshold. Some argue that hardened missile silos or complex arsenals located in mountains and caves may call for a tactical nuclear weapon. Again though, this is a nuclear strike and perhaps a pre-emptive one at that. Bunker buster missiles are more apt to handle the problem without the international condemnation of nuclear use. Can the United States lead the world in non-proliferation when developing nuclear weapons that are more acceptable to use? I think not.
Overall, tactical nukes pose no benefit when compared against strategic nuclear weapons and conventional weapons. The development of these tactical nukes will lead to more nuclear use, not a greater deterrence. Lieber and Press must understand that crossing the nuclear threshold is not relative. Once you detonate a nuclear weapon, it does not matter if you crossed that nuclear line by 50 ft (tactical) or 100 ft (strategic).