Russia continued its bombardment of Ukraine with drone and missile strikes, and the US weighed the possibility of additional economic sanctions on Russia, including secondary sanctions against states trading with Russia. Debates among the Washington cognoscenti about possible peace settlements focused on two “baskets” of topics: what kind of “land swap” might be agreeable to Ukraine and Russia and what sort of security guarantees would be necessary for a postwar Ukraine. Amid all of this, one elephant in the room received little attention: the status of nuclear weapons and nuclear deterrence in future relationships between Ukraine and Russia and between Russia and NATO.

President Donald Trump posted on social media in late July 2025, that Dmitri Medvedev, Russia’s former president, was a “failed former President of Russia” who had better “watch his words.” Trump was responding to earlier remarks by Medvedev, after Trump threatened economic sanctions against Russia unless Russian President Vladimir Putin agreed to a temporary ceasefire and expedited peace talks with Ukraine.

In the earlier exchange, Medvedev called Trump’s ultimatum about peace talks a threat and a step toward war. Most recently, Medvedev again warned against nuclear danger by referring to the American television series The Walking Dead and reminded Trump that Russia retains the Soviet “Dead Hand” system for automatic nuclear launch even under the most extreme postattack conditions.

In response, President Trump posted on social media that he ordered two nuclear submarines to be repositioned in response to Medvedev’s threats. Trump said he ordered the submarines “to be positioned in the appropriate regions, just in case these foolish and inflammatory statements are more than just that.” In addition, the President noted that “[w]ords are very important and can often lead to unintended consequences. I hope this will not be one of those instances.”

Nuclear submarine movements are among the most highly classified information pertinent to military operations. If the reference was to American nuclear ballistic missile submarines (SSBN), this public announcement was unprecedented.

At one level, these interchanges between Medvedev and Trump are as much performative as they are substantive. During the early stages of Russia’s war against Ukraine beginning in February 2022, Putin issued frequent warnings about the possibility of Russian nuclear first use in response to actions taken by the North Atlantic Treaty Organization (NATO) that might be unacceptable to Russia. These warnings were dismissed by many Western political leaders and military experts as bluff to conceal Russia’s frustration at the prolonged military deadlock it faced in Ukraine, as well as distractions from looking too closely at Russia’s disappointing battlefield performances.

As Russia’s military operations on the ground seemed to improve in 2024 and 2025, nuclear threats became less frequent and less explicit. At present, Russia seems confident of maximizing its forward progress in military reach and operational control over the Donbass and other districts in the east and south of Ukraine.

Even a “small” nuclear war fought with tactical nuclear weapons would be a self-defeating endeavor for Russia. Fighting a conventional war under the shadow of possible nuclear escalation is sufficiently risky. If Russia were to cross the bridge into nuclear first use there would be a strong likelihood of a NATO nuclear response.

Russians need to interrogate their own military literature from the Cold War with respect to the challenge of conducting military operations in a nuclear environment. Troops seeking an operational breakthrough against enemy defenses would be fighting against the prompt and delayed effects of nuclear detonations that slow operational movement, inflict significant numbers of casualties, and corrupt the coordination and cohesion of combined arms. The Soviet Union could draw upon its ideological indoctrination and favorable memories of its victory in the Great Patriotic War (World War II) to maintain morale and avoid mass desertion, Russia cannot.

Nor would the economy of Europe, including Russia, survive anything beyond the very restrictive use of a few ultra-low-yield or low-yield in the sub-five kiloton range. In today’s world of social media and globally transmitted visual images, the meltdown of major financial and other institutions in Europe would trigger a global crash of markets, disrupt supply chains, let loose armed formations of criminals, and drive many leading politicians to abdication. Some in NATO might hope that Putin’s mistaken decision for nuclear first use would finally convince Russia’s military and security forces to overthrow their president and sue for peace, but Putin is not Lenin, and he is as likely to double down on escalation as he is to acquiesce to a nuclear ceasefire.

And therein lies the second danger, escalation to strategic nuclear war between the United States and Russia. Putin might calculate that he could hive off the nuclear deterrents of the British and French from their American allies and bully the former into submission while frightening the American government and public with separate threats of mass destruction. This would be a dangerous miscalculation because the nuclear forces of the United States are politically and operationally coupled to those of their European allies.

American nuclear weapons and American personnel deployed in Europe are effectively tied to the continent under Article V of the NATO charter. The idea that selective use of tactical nuclear weapons in Europe by Russia could be sealed off from wider and more deadly destruction, is beyond optimism.

In addition to misplaced optimism about escalation control during a major European war, there is also a lack of appreciation for the challenge of skillful crisis management that might avoid war altogether. Experience teaches that the requirements for nuclear and other crisis management include shared understandings and expectations about the risks of war and a willingness to consider the danger of misperceptions held by leaders in stressful situations. They may misjudge other national leaders as irrevocably committed to acts of conquest or aggression, when in fact those other heads of state may be undecided about their final judgments for or against war.

Communication between and among leaders may be incomplete and intelligence assessments can be blinkered by insufficient information or political bias. Examples of these and other maladies in crisis are provided by the July crisis of 1914 leading to the outbreak of World War I, the Cuban missile crisis of 1962, and by numerous other crises.

Russians playing with the rhetoric of Armageddon are legitimizing nuclear coercion in a time of troubles. The arrangement of a prompt ceasefire and peace agreement between Ukraine and Russia is of the highest significance for many reasons. These include putting an end to the loss of life and the destruction of national infrastructure. This objective should be pursued with aggressive diplomacy and without the distraction of references to the possibility of a war that would have no precedent in its capacity to do irreparable harm to civilization.

Steve Cimbala is a Senior Fellow at the National Institute for Deterrence Studies.

Nuclear Danger Remains in Ukraine Peace Settlement was originally published on Global Security Review.

The simulated conflict ended without regime change in Pyongyang, allowing Kim Jong Un to claim a political victory. While avoiding nuclear escalation may seem prudent, such an outcome could deal a lasting blow to the credibility of America’s extended deterrence in East Asia.

The Guardian Tiger scenario should not be dismissed as an academic exercise. It reveals a critical vulnerability in the psychological foundation of deterrence: the perception among adversaries and allies of American willingness to use nuclear weapons in defense of its partners. If allies conclude that Washington will not cross the nuclear threshold even after a nuclear attack, they may question the value of the nuclear umbrella. Adversaries, meanwhile, may learn that nuclear coercion, carefully calibrated, can succeed.

In the simulation, North Korea escalated to a tactical nuclear strike against a South Korean Navy destroyer in the East Sea (Guardian Tiger I) and later against the Chinhae naval base (Guardian Tiger II), home to the Republic of Korea Navy’s Submarine Force Command and occasionally used for allied submarine visits. According to the report, American leaders debated nuclear retaliation but settled on conventional “pulsed” strikes.

In a real-world scenario, such strikes could plausibly involve precision-guided munitions from long-range bombers like the B1-B and Tomahawk cruise missiles launched from Arleigh Burke-class destroyers, aimed at targets such as missile transporter-erector launchers, hardened artillery positions along the DMZ, and command-and-control facilities near Pyongyang. In the exercise, the US stopped short of regime change, seeking to avoid further nuclear escalation and prevent a direct war with China—a decision that would have allowed Pyongyang to absorb the damage, count the survival of its regime as a strategic win, and enter negotiations from a stronger position.

Extended deterrence depends on more than military capability. It is rooted in the belief, shared by allies and adversaries alike, that the United States is willing to defend its partners by all means necessary, including nuclear weapons. An American failure to respond in kind to North Korean nuclear use would plant seeds of doubt. Japanese and South Korean leaders could begin to question whether Washington would truly “trade Los Angeles for Tokyo or Seoul” if the stakes involved limited nuclear use rather than an existential threat to the United States.

That doubt could trigger cascading effects. Calls in Seoul’s National Assembly for indigenous nuclear weapons, expanded production of the Hyunmoo‑4 ballistic missile, and pressure on Tokyo to more seriously pursue nuclear sharing arrangements have already entered the political debate.

This concern is amplified by North Korea’s 2022 nuclear weapons law, which openly authorizes preemptive nuclear strikes in scenarios ranging from an imminent attack on leadership to undefined overwhelming crisis situations. Analysts note that the law’s language effectively lowers the threshold for nuclear use, implying tactical employment to repel invasion and seize the initiative in war. Rather than viewing nuclear use as a desperate last resort, Pyongyang now appears willing to employ such weapons early. For example, a low‑yield detonation against South Korean or American forward-deployed forces to shock Washington and Seoul into political concessions.

The challenge grows sharper in the event of a dual contingency: simultaneous crises on the Korean Peninsula and in the Taiwan Strait. Guardian Tiger II simulated such a scenario, with China launching a multi-domain assault on Taiwan while North Korea escalated on the peninsula. In such a real-world situation, US Indo-Pacific Command could be forced to divert the USS Ronald Reagan Carrier Strike Group from Yokosuka to the waters east of Taiwan, deploy B‑52H bombers to deter Chinese operations, and even consider repositioning some Terminal High Altitude Area Defense and Patriot missile defense batteries from South Korea to protect American assets in Okinawa and Guam.

Such shifts illustrate how a stretched American posture could reduce missile interception capacity on the peninsula and temporarily remove some nuclear-capable platforms from immediate Korean defense. North Korea could calculate that Washington, already balancing a larger confrontation with China, would avoid nuclear escalation in Korea to conserve resources and limit the risk of an all-out US-China war.

The political and strategic consequences would ripple across the region. In Seoul, public and elite opinion could shift sharply toward developing an independent nuclear arsenal—something 71 percent of South Koreans already support. South Korea’s nuclear latency, widely assessed by proliferation experts, suggests it could potentially produce a weapon in as little as 6 months if political consensus formed.

In Tokyo, the debate over counterstrike capabilities, missile defense expansion, and potential nuclear sharing with the United States would intensify, potentially accelerating deployment of Tomahawk missiles and further integration of F‑35A fighters, which, in the US fleet, are being certified for B61‑12 nuclear bombs, into allied defense planning. Beijing, meanwhile, could seize the opportunity to position itself as a stabilizing broker, offering to mediate between Seoul and Pyongyang while shielding the latter from full international accountability, further eroding American influence.

Avoiding nuclear escalation in a limited-strike scenario is understandable, but Washington cannot afford such a decision to be interpreted as weakness. Strengthening deterrence credibility in Northeast Asia will require more than declaratory statements. Clear and credible red lines for nuclear use must be communicated both publicly and privately. Integrated nuclear-conventional planning with allies should ensure that flexible response options, from proportionate nuclear strikes to overwhelming conventional retaliation, are executable on short notice. Contingency planning must explicitly account for simultaneous conflicts in Korea and Taiwan, with pre-positioned munitions, dispersed basing arrangements for nuclear-capable aircraft, and rotational deployments of dual-capable ships and submarines to maintain strategic presence even under force diversion.

Equally important is sustained alliance signaling. These include high-visibility joint exercises like the US-ROK Freedom Shield exercises, regular port visits by nuclear-capable submarines, and trilateral missile tracking drills with Japan. These measures reassure allies, complicate adversary calculations, and demonstrate that any nuclear use will incur unacceptable costs.

The Guardian Tiger exercises are valuable not because they predict the future, but because they reveal how quickly deterrence can fray in the fog of crisis. A single decision to refrain from nuclear retaliation, however understandable at the time, could reverberate for decades and reshape the strategic balance in East Asia. In the nuclear age, preserving deterrence means guarding against both uncontrolled escalation and the perceptions of hesitation that could invite it.

Dr. Ju Hyung Kim, President of the Security Management Institute, a defense think tank affiliated with the South Korean National Assembly, is currently adapting his doctoral dissertation, “Japan’s Security Contribution to South Korea, 1950 to 2023,” into a book.

A Nuclear Umbrella in Peril: Lessons from North Korea’s Escalation Scenarios was originally published on Global Security Review.