"My work becomes the deterrent, not so much the products of my work," said Martz, an advocate of the virtual swords concept. - from John Fleck's Albuquerque Journal Article.
"...that the deterrent benefit accrues through the weapons existence and is robust across disparities in the technical details" - from the Arms Control Wonk
The issue that connects these observations to news is Plutonium Pit Production in Los Alamos (John is a far better explainer, so consult his article for the details). More importantly than that, they are comments on what new plutonium pit production means for the United States nuclear stockpile, and the aims of nuclear weapons programs.
The big justification of new production is that the United States no longer needs to have the weapons on hand, but that the production capabilities should still be present. This is interesting logic, and it's quite distance from defense thought about terrorism. Nuclear deterrent requires fixed targets, and somewhat rational people who can be effectively deterred. Insurgencies, terrorists, and guerrillas all seem to be off limits for the power of nuclear force, and so nuclear policy as deterrent is directed at nations and governments. Nothing new, but it's worth clarifying that the policy, as it stands, is focused on deterring wars between states, and not wars within states or asymmetric war against states. The threat of a nuclear attack does little, if anything, for those other scenarios.
This is the virtual sword, a new outlook which is a step back from the days of Mutually Assured Destruction, and looks instead at conflict with an eye towards high costs, but not necessarily world ending ones. A nation in conflict with the US will have to weigh the cost of a nuclear attack, of some scale, against pursuing that conflict. This has worked for all conflicts between nuclear nations, which have been blissfully few; Pakistan v. India being the exception, and then war has been halted and not accelerated but the presences of nuclear arsenals and a very, very, very high cost to waging war beyond conventional means. Nuclear retaliatory force, and the knowledge that that force will be replenished, allows nukes to enter into the algebra of war, moving it from a last ditch, too-hard-to-consider option to an incredibly costly and futile option. Nations are unlikely to risk either, but I see this as a step down for the US (not a bad thing, necessarily); cold war capabilities guaranteed a tremendous amount of destruction, should the wrong sequence of events happen. This new rationale, this Virtual Sword means that any state risking armed conflict with the United States will still have to worry about a nuclear attack; the attack will render the conflict moot, and doesn't entail the most terrifying degree of destruction imaginable.
Nuclear conflict will still not be an option considered; the weapons capability is such that it will be on board as a possibility to back away from, to step down from. More notably, though, a reduced capability (in terms of numbers) but continued research means two things. One, that nuclear power will stay relevant, should an effective defense be devised, and two, that the arsenal is not enough to attack fifteen nations at once (as Cold War plans intended). Sheer volume is not what is needed for a nuclear arsenal in the future, and this necessitates new plans in hypothetical nuclear war planning.
This brings us to the Arm's Control Wonk's quote. Nuclear weapons are nuclear weapons, and as deterrent little more than being nuclear and deliverable is needed. Any weapon that is developed that affects this policy will meet both of those requirements, and so the details, the nitty-gritty of what exactly each can do, how deep the blasts can go, and how particularly devastating each weapon will be, are more or less irrelevant to the politics of the weapons use. Not that the details of a weapon are purely military considerations; they aren't, and that attitude is damaging. But whenever nuclear weapons are considered, they are to be considered as nuclear weapons, and the threat of usage of nuclear weapons is a political aspect, that varies little whether or not the depth penetrated is 3 meters or 50. Nuclear deterrent just requires that nuclear weapons capabilities exist, and be perceived as threatening enough to prevent a state from risking war, and especially war on a large scale.