Recent media reports suggesting that President Obama’s considering embracing a no-first-use pledge in US nuclear declaratory policy have certainly rekindled the debate over the wisdom of such a move. The debate’s not new, and resonances of its earlier rounds abound. Over at Arms Control Wonk, Michael Krepon has penned a couple of thoughtful pieces (here and here), essentially supporting the notion of a no-first-use policy—just not yet. On the other side of the debate, Elbridge Colby’s argued that a no-first-use declaration would be a deep strategic error. Andrew Shearer’s argued a similar line over at War on the Rocks.

In arms control terms, no-first-use pledges have a superficial attractiveness. For one thing—if they could be taken at face value—they would imply an important raising of the nuclear threshold. If all nine current nuclear weapon states were to embrace them, none would ever use nuclear weapons first in a conflict. And the essential role of nuclear weapons would be limited to deterring, and responding to, an adversary’s use of nuclear weapons in violation of that pledge.

But can they be taken at face value? One of the central problems with a no-first-use pledge is that it’s inherently incredible. Such a pledge says that a nuclear weapon state is content to lose a war at the conventional level without resorting to nuclear weapons. Perhaps that’s the case with some limited conventional conflicts fought over peripheral rather than core interests. But it’s not true in relation to all conventional conflicts. All of the nuclear weapon states have some interests the loss of which they would regard as intolerable. Such prospect of loss would excite resort to nuclear weapons. If it didn’t, why would they have built them in the first place?

The second problem is one of strategic utility. If nuclear weapons are useful in deterring major war, why are we so anxious to ensure they deter only nuclear use? NATO strategists in the days of the Cold War used to argue plausibly that theatre- and tactical-range nuclear weapons helped offset the possibility of Soviet conventional aggression by making it more difficult for the Warsaw Pact to concentrate its tank armies. Any such massing of forward-deployed armour would be a potential target for a NATO nuclear weapon. In short, NATO’s option of crossing the threshold first helped to lengthen the odds that it would ever need to do so. NATO’s logic then remains just as compelling today for any nuclear weapon state which feels itself conventionally outgunned.

Even those nuclear weapon states confident about their own conventional strength might well see a role for nuclear weapons in constraining an adversary’s options. The US found itself in exactly that position in the early 1990s, leading the multinational force engaged in expelling Saddam’s forces from Kuwait. Veiled US threats then that Washington would regard any Iraqi use of weapons of mass destruction—essentially chemical weapons—as opening the door to possible US nuclear weapon use, were designed to constrain Iraqi options and leverage the multinational force’s conventional advantage.

Then there’s a third problem—assurance. A US no-first-use pledge would play merry havoc with its extended nuclear assurances to its allies. Allies would worry about both of the first two problems: that a US which was serious about its no-first-use pledge might be more inclined to see their interests as peripheral rather than vital; and that they’re more exposed to shifts in regional conventional force balances than is the US itself. That’s broadly true for all US allies around the Eurasian rimlands, but the rapid growth of Chinese conventional power in Asia makes this factor particularly telling in Australia’s own region.

For all those reasons, a sudden step towards a no-first-use pledge by an American president in the last six months of his office would be a worrying development. True, the 2010 US Nuclear Posture Review pointed to a future in which the US would ‘seek to reduce the role and numbers of nuclear weapons’. But Washington balked at making a ‘sole purpose’ declaration—essentially a declaration that the sole purpose of nuclear weapons was to deter any use of nuclear weapons by an adversary—during that Review. And it’s hard to argue that nuclear weapons have become more irrelevant in the years since. There’s strategic value in the current policy. That, by the way, isn’t a pledge to use nuclear weapons first; it’s merely a refusal to pledge not to do so. That position retains the possibility of first use—which is probably unappetising for some, but fulfils the tests of credibility, deterrence and assurance. If we have to live through the nuclear age, let’s at least make sure the weapons make a positive contribution to international security.