The current debate over American declaratory policy is largely bifurcated between advocates of the status quo— a position often termed “calculated ambiguity”—and proponents of no-first-use (NFU). Under current policy, the United States reserves the right to employ nuclear weapons “to defend the vital interests of the United States or its allies and partners.” Under a policy of no-first-use, the United States would make a blanket commitment not to use nuclear weapons first. Neither of these declaratory policies is appropriate.
 No U.S. president would even consider using nuclear weapons in any of these scenarios—as potential adversaries are no doubt aware. Even an attack against key U.S. military space assets would, by itself, fall far short of the nuclear threshold (not least because there would be no loss of life). At best, making implicit threats that are incredible does not enhance deterrence; at worst, it could damage security by calling the credibility of other, more serious nuclear threats into question.Calculated ambiguity is too permissive. The threat to employ nuclear weapons in the defense of “vital interests” is deliberately vague, invoked to try and enhance deterrence by creating significant uncertainty among adversaries about the circumstances in which the United States might employ nuclear weapons (though Washington has pledged explicitly not to use nuclear weapons against non-nuclear-weapon states in compliance with their nonproliferation commitments). The problem is that the United States defines its vital interests very broadly. In the past decade, for example, the President or the Secretary of State has identified as vital interests, “the stability, safety and security of our space systems,” “the peaceful management of maritime disputes,” and “helping the young democracies” of Latin America.
The expansiveness of current policy has other significant drawbacks. It undermines American efforts to demonstrate a commitment to work in good faith toward a world without nuclear weapons, as legally required by the 1968 Nuclear Nonproliferation Treaty. It also sets an example that other nuclear-armed states might follow in carving out greater—and potentially more dangerous— roles for nuclear weapons. Indeed, some have already done so. For example, when India abandoned its NFU policy in 2003 by permitting a nuclear response to chemical or biological attacks, it was, according to Scott Sagan, “copying the United States.” As a result, there would probably be both security and political benefits to narrowing U.S. declaratory policy.
No-first-use is the most commonly touted alternative to calculated ambiguity. While a desirable goal, it suffers from its own problems. The case for NFU rests on the argument that U.S. conventional superiority precludes any need for the United States to threaten nuclear employment in response to nonnuclear threats. While it is certainly true that a sufficient degree of conventional superiority could enable a switch to NFU, it is unclear whether the United States enjoys the required margin in all key theaters today and even more unclear whether it will do so in the future.
Conventional deterrence depends on the local—not the global—balance of conventional forces. It can fail when a potential aggressor believes it can wage a quick and relatively painless war to seize territory, say, and thus present its opponent with a fait accompli that would require a bloody and prolonged campaign to reverse.
Even today, the United States and its allies lack local conventional superiority in at least one region of potential conflict—the Baltic (even as they are superior in Europe as a whole). As a result, there is legitimate concern that Russia might try to seize NATO territory in the expectation that the alliance lacks the stomach for a prolonged campaign to restore it. To be sure, NATO’s weakness around the Baltic is a political choice that could be reversed (indeed, the alliance is starting to deploy more conventional forces to the region). Elsewhere, however, conventional imbalances could arise that would be much more difficult to undo. Most significantly, China may achieve conventional superiority in the West Pacific in the not-too-distant future. If it does and if the United States wishes to continue to uphold its commitment to regional allies—Taiwan, in particular—then Washington will have little choice but to rely on threats of nuclear first-use.
A no-first-use policy is, therefore, not a viable option for the United States right now—although Washington can and should take steps to promote it. The United States should, for example, seek to work cooperatively with both Russia and China to achieve a durable balance of conventional forces in key theatres so that both sides feel secure. Of course, making progress on this agenda—let alone achieving it— will be exceptionally challenging. But, such challenges need not prevent other adjustments to declaratory policy in the near future.
Specifically, the United States should pledge not to employ nuclear weapons except to defend itself, its allies or its partners from threats to their very existence. In articulating this policy, the United States should emphasize that, because of the possibility of escalation, it considers that any use of nuclear weapons against itself, its allies, or its partners would constitute an existential threat. But, because existential threats are not limited to nuclear use, this declaratory policy would allow the United States to employ nuclear weapons to defend allies from the most extreme nonnuclear threats.
Such a policy would offer two advantages over the status quo. First, it would be more moral and more credible than calculated ambiguity. Given the long tradition of the non-use of nuclear weapons, the clear U.S. interest in extending this tradition, and the numerous potentially enormous costs and risks associated with nuclear use, it is difficult to imagine the United States employing nuclear weapons in response to anything less than an existential threat. Credibility would, therefore, be best served by recognizing this reality in declaratory policy.
Second, the proposed policy would probably be seen by the international community as more legitimate than calculated ambiguity. For starters, it would represent a real and significant reduction in the role that the United States assigns to nuclear weapons. Russia has already adopted such a policy, which is consistent—or at least not inconsistent—with the one ruling on the legality of nuclear use by an international court. Specifically, in a 1996 ruling (albeit an advisory and non-binding one), the International Court of Justice concluded that “the threat or use of nuclear weapons would generally be contrary to the rules of international law.” But, the court was unable to “conclude definitively whether the threat or use of nuclear weapons would be lawful or unlawful in an extreme circumstance of self-defense, in which the very survival of a State would be at stake.” While this ruling, which both disarmament and deterrence advocates have reasons to ignore, does not exactly bless the proposed policy, it doesn’t undercut it either.
To be sure, a pledge by the United States to limit the role of nuclear weapons to defending against existential threats would probably not attract much praise by non-nuclear-weapon states, many of which would now accept nothing less than immediate negotiations on a treaty to eliminate nuclear weapons as an acceptable marker of progress toward disarmament. But, with a carefully designed and concerted diplomatic effort, the United States may be able to earn credit for this new policy while balancing the potentially competing security objectives of sustaining the nonproliferation regime and defending its allies.
 United States Department of Defense, Nuclear Posture Review Report (April 2010), http://www.defense.gov/Portals/1/features/defenseReviews/NPR/2010_Nuclear_Posture_Review_Report.pdf
 Lisa Daniel, “Defense, State Agree to Pursue Conduct Code for Outer Space,” Armed Forces Press Service, 18 January 2012, http://archive.defense.gov/news/newsarticle.aspx?id=66833; Secretary of State John Kerry, “Remarks,” Brunei, 2 July 2013, http://www.state.gov/secretary/remarks/2013/07/211502.htm; President George W. Bush, “President’s Radio Address,” 10 March 2007, https://georgewbush-whitehouse.archives.gov/news/releases/2007/03/text/20070310.html
 Scott D. Sagan, “The Case for No First Use,” Survival 51:3 (June-July 2009): 163-182, at 176.
 Michael S. Gerson, “No First Use: The Next Step for U.S. Nuclear Policy,” International Security 35:2 (Fall 2010), 7-47.
 Michael S. Gerson, “Conventional Deterrence in the Second Nuclear Age,” Parameters (Autumn 2009), 32-48.
 David A. Shlapak and Michael W. Johnson, Reinforcing Deterrence on NATO’s Eastern Flank: Wargaming the Defense of the Baltics (Santa Monica: RAND Corporation, 2016), https://www.rand.org/content/dam/rand/pubs/research_reports/RR1200/RR1253/RAND_RR1253.pdf
 George Perkovich, Do Unto Others: Toward a Defensible Nuclear Doctrine (Washington, D.C.: Carnegie Institute for International Peace, 2013), http://carnegieendowment.org/files/do_unto_others.pdf
 Military Doctrine of the Russian Federation, August 2015, https://www.offiziere.ch/wp-content/uploads-001/2015/08/Russia-s-2014-Military-Doctrine.pdf
 International Court of Justice, “Legality of the Threat or Use of Nuclear Weapons,” 8 July 1996, http://www.un.org/law/icjsum/9623.htm
 Ben Doherty, “UN votes to start negotiating treaty to ban nuclear weapons,” Guardian (UK), October 27, 2016, https://www.theguardian.com/world/2016/oct/28/un-votes-to-start-negotiating-treaty-to-ban-nuclear-weapons
This article originally appeared in International Security Studies Forum