In June 2025, Ukraine’s security services staged an audacious strike inside Russia. They infiltrated the country and hid short-range attack drones in cargo trucks near a slew of Russian air bases as far away as the Amur region on the border with China. Most of these bases were home to Russian strategic heavy bombers—aircraft capable of carrying nuclear weapons. Using Russia’s mobile phone network, Ukrainian operatives remotely launched the drones, successfully destroying at least ten of the bombers and damaging a total of 41 planes, including some used for nuclear command and control, according to Ukrainian assessments.

Known as Operation Spider’s Web, this assault was a remarkable gambit. The most significant aspect of the attack, however, was not its astonishing cost ratio—as one analyst put it, “a single drone costing just $500 destroyed a strategic bomber worth tens of millions of dollars”—or its ingenuity in hijacking Russian telecommunications, but the fact that it could happen at all. As part of its long-standing doctrine, Moscow had insisted that a conventional attack on its strategic assets could provoke a nuclear response. But that did not stop Kyiv. Ukraine was willing to go after Russia’s nuclear capabilities, and Russia was unable to prevent their destruction.

The Ukrainian operation was a spectacular example of a wider trend: nuclear deterrence is not working. Countries have long assumed that the possession of nuclear weapons was the surest guarantee of their security. Indeed, many observers saw the full-scale Russian invasion of Ukraine in 2022 as proof that Kyiv had erred in 1994 by agreeing to give up the nuclear weapons it inherited from the Soviet Union. If Ukraine had the bomb, they suggested, Russia would not have dared to attempt such an attack. Similarly, if Iran had already developed its own arsenal of nuclear weapons, Israel and the United States would not have been able to strike the country as they have since February, killing Iranian leaders and leveling Iranian military infrastructure. From that argument inevitably flows the conclusion that more countries will reasonably want nuclear weapons as insurance against aggression. States ultimately need these weapons of mass destruction to deter their greatest adversaries.

But recent conflicts more clearly advertise the reverse. Ukraine is not just hitting targets deep within Russia but also targets directly related to Russia’s nuclear capabilities. Iran and its proxies have repeatedly attacked Israel, which is widely believed to possess nuclear weapons. Tehran has aimed missiles and drones at Israeli cities and even nuclear facilities. And India and Pakistan, which both possess nuclear weapons, engaged in the most serious conflict between the two countries in this century, attacking far across each other’s borders in May 2025. In all these cases, the possibility of nuclear escalation and retribution did not prevent conventional and hybrid warfare. Indeed, state and nonstate actors are in effect calling the bluff of nuclear-armed powers.

Nuclear weapons can appear impotent in the face of sustained conventional and hybrid attacks; in today’s warfare, an arsenal of nuclear-tipped intercontinental ballistic missiles, a flotilla of nuclear submarines, and squadrons of strategic bombers can do little to deter salvos of cheap drones—as long as those nuclear states remain unwilling to use their weapons. That should give pause to both existing nuclear powers and those that may want to acquire the weapons.

The strength of the nuclear taboo was tested in the early months of Russia’s invasion of Ukraine, when Russian President Vladimir Putin evidently came close to using tactical nuclear weapons to stop a rout of his troops in southeastern Ukraine. He was prevented, it seems, by a combination of advice from his own military leaders and public pressure from his Chinese and Indian counterparts—and doubtless private pressure from Washington. Although the taboo is not an absolute bar against the use of nuclear weapons, leaders who flirt with the idea of deploying them experience heavy pushback. They also must reckon with the fact that they would be remembered as only the second human being to drop the bomb in combat, earning them a dauntingly infamous place in history.

For nuclear states, the lessons of this moment must be jolting. State and nonstate adversaries are increasingly willing and able to hit nuclear powers with conventional weapons. That scrambles the traditional logic of nuclear deterrence. Deterrence by threat of nuclear retaliation, the traditional tool that has ensured nuclear stability for decades, is weakening. Deterrence by denial—that is, discouraging an attacker by making an attack seem futile—may become more valuable.

That approach will demand different priorities for governments. Instead of investing vast sums in modernizing existing platforms, nuclear states could be better served by strengthening defenses around their nuclear facilities, focusing on resilience rather than nuclear capacity. And they should find ways to uphold and strengthen norms governing conventional targeting—by pledging, for instance, never to strike nuclear power plants and military nuclear facilities. These measures will help slow escalation during crises when warring parties feel emboldened to strike enemy nuclear facilities. For nonnuclear states, the waning of traditional nuclear deterrence should offer a more general warning. Rather than bringing the certainty of security, the bomb may simply invite new and disconcerting forms of peril.

THE WANING OF DETERRENCE

Beginning in the Cold War, the United States and the Soviet Union, now Russia, have deployed a triad of nuclear systems to both threaten and deter their rivals: ground-based intercontinental ballistic missiles, ballistic missiles launched from submarines, and heavy bombers. These systems can deliver warheads at a range beyond 3,400 miles, which is the basis for describing them as “strategic offensive forces.” The United States can directly target the Russian homeland, and the Russians can target the continental United States. China’s rapid nuclear buildup in recent decades has sought to bring Beijing on par with Moscow and Washington. By........

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