Giles David Arceneaux
As the war in Ukraine moves past the two-and-a-half-year mark, an enduring question has once again returned to the forefront of debates: where are Russia’s red lines for nuclear escalation?
Since launching a surprise incursion into Russia’s Kursk region on August 6, 2024, Ukraine has seized over 1,300 square kilometers of Russian territory. The Kursk offensive caught both Russia and Ukraine’s partners by surprise and has provided Ukraine with a much-needed shift in momentum in the Russia-Ukraine war.
Ukraine’s rapid gains in the Kursk offensive have already produced significant strategic effects. The operation has boosted domestic morale and international confidence in Ukraine’s ability to win, provided a bargaining chip that Ukraine can use in future negotiations with Russia, and placed pressure on the Kremlin to redirect forces from its offensive campaign in the east to stymie Ukraine’s battlefield gains.
Remarkably, though, Russia’s response to the Kursk offensive has been unusually muted. Despite failing to deter the first invasion of Russian territory since World War II, observing a strategic boost for Ukraine’s war effort, and potentially facing internal dissent within Russian President Vladimir Putin’s regime, the Kremlin has actively downplayed the importance of the fight in the Kursk region.
The tepid response to an incursion on Russian territory is especially notable in light of Russia’s repeated threats to use nuclear weapons throughout the war. The lack of a significant rhetorical or behavioral response casts doubts on the credibility of Russia’s nuclear threats and generates a question for analysts: if an attack on Russian territory did not prompt a nuclear response, what could possibly serve as a trigger for nuclear escalation?
Despite the lack of notable Russian escalation in response to the Kursk offensive, it would be a mistake to simply dismiss Russia’s nuclear threats wholesale. Instead, the more compelling lesson learned from the Kursk offensive is that Russia’s threshold for nuclear escalation is higher than Moscow would like its adversaries to believe. Although the location of Russia’s red lines remain opaque, Russia’s nuclear forces and doctrine create real risks that must be carefully considered. Rather than categorically rejecting the possibility of nuclear escalation, Western supporters should use such scenarios to update their understanding of escalation risks and opportunities to support Ukraine.
An Atypical Response
The lack of a major Russian response to the Kursk offensive stands in stark contrast to the typical behavior exhibited by the Kremlin since its February 2022 invasion of Ukraine.
Throughout the war in Ukraine, Russian leaders have continuously issued nuclear threats in response to a wide range of actions. For example, in response to Western sanctions after Russia’s full-scale attack, Putin publicly announced that he had placed Russian nuclear forces on alert. Russia also responded to the prospect of Sweden and Finland joining NATO with warnings of nuclear deployment in the Baltic region. Military support to Ukraine has produced additional nuclear saber rattling, both in response to general Western support and specific platform deliveries. In short, Russia has repeatedly threatened nuclear use in response to everything from economic pressure to NATO expansion and military threats.
Given this history of nuclear saber rattling in response to large and small provocations alike, the Kursk offensive’s rapid seizure of Russian territory seems like a most-likely case for generating renewed nuclear threats. In this case, however, such threats have not yet come to pass.
Although Russia has implied that a nuclear power plant near the fighting in Kursk might experience a mishap, overt statements threatening a response with nuclear weapons have been notably absent. Instead, Putin simply referred to the Kursk attack as a “large-scale provocation” and described the Russian response as a “counter-terrorism operation.”
Russian Foreign Minister Sergey Lavrov did issue a nuclear threat on August 27, 2024, but this threat came in response to debates over whether Western states would enable Ukraine to use long-range weapons against Russian territory. By doing so, Russian leaders have effectively skipped over the Kursk offensive to resume declaring nuclear threats elsewhere.
The lack of Kursk-related nuclear threats is made even more surprising by two operational developments in Russia during the war in Ukraine.
First, Putin delivered a speech in October 2022 that lowered the threshold for nuclear to when the “territorial integrity” of Russia was at stake. With 1,300 square kilometers of Russian territory under Ukrainian control, this threshold has certainly been breached.
Second, the Kursk incursion came only days after Russia concluded a three-stage series of drills simulating the deployment of tactical nuclear weapons in combat. Rather than view these exercises as a robust deterrent, Ukraine elected to escalate the conflict and fight Russia on its own territory.
Despite clear reasons for Moscow to return to its playbook and threaten nuclear escalation, though, no such response has occurred. And so, the question remains: where are Russia’s nuclear red lines?
Reevaluating the Threshold
In the absence of even a rhetorical nuclear response to Ukraine’s Kursk offensive, outside observers are left to speculate about the conditions under which Russia would resort to nuclear weapons use.
The dominant reaction to the lack of a Russian response is the belief that Putin’s nuclear red lines are a bluff. This sentiment is shared by a broad group, ranging from Western analysts to Ukrainian President Volodymyr Zelenskyy. Given the absence of a Russian response to an attack on its territory after two and a half years of nuclear threats, this perspective is not entirely unreasonable.
In practice, however, two problems exist for this school of thought.
First, the discussion of Russian red lines as a binary condition—either they exist, or they do not—provides the wrong framing for the problem. Russia possesses the world’s largest nuclear arsenal and a first-use nuclear doctrine, both of which are clearly designed to enable nuclear use. The question is therefore not whether Russia possesses nuclear red lines, but rather where those red lines are located.
Russia’s nuclear threats throughout its war in Ukraine have been intentionally vague. The purpose of Russian threats has not been to specify the exact conditions under which nuclear weapons would be used, but rather to slow Western support to Ukraine by inducing uncertainty and creating fears of uncontrollable nuclear escalation. The Kursk offensive shows that the threshold for nuclear use is higher than Russia would like its adversaries to believe, but it does not necessarily indicate that Russia’s threats are completely empty. The risks are real, and policymakers must remain mindful of the various pathways through which nuclear escalation remains a danger.
Second, the total rejection of Russian nuclear threats creates a risk of complacency that may inadvertently increase the likelihood of nuclear escalation. If the West becomes unreservedly emboldened to challenge Russia while Putin’s supporters pressure him to escalate—potentially even creating implicit threats to Putin’s regime—the combination of external and internal threats could inadvertently produce strong incentives for nuclear use. Indeed, Western support for Ukraine has been intentionally slow and methodical to avoid exactly this type of outcome.
The success of the Kursk offensive should not lead to the dismissal of all Russian nuclear threats as bluffs. Instead, it should serve as a data point that calibrates policymakers’ perspectives on where Putin’s red lines are and how to manage and mitigate those risks.
Lessons in Escalation Risks
The lack of any meaningful Russian nuclear response to the Kursk incursion does not exactly delineate Russia’s nuclear thresholds, but it is nevertheless informative. Two important lessons for the next stages of Western support to Ukraine emerge from the nuclear-related developments of the Kursk offensive, revealing both good and bad news.
First, the threshold for nuclear use remains high, and it is likely higher than both Russian and Western leaders may have originally believed. This is the good news. Given the costs associated with the use of nuclear weapons—such as isolation as an international pariah state and the potential for US conventional military strikes against Russian forces in Ukraine—Russia would be unlikely to whimsically resort to nuclear use unless left with few other options. Nuclear weapons are the ultimate guarantor of state and regime survival, so the possibility of nuclear use remains real. But, as the Kursk offensive has revealed, there is more space for the West to operate under the nuclear shadow than may have been believed at the onset of the war in Ukraine.
Second, the exact location of Russia’s red lines remains unknown. This is the bad news. The ambiguity surrounding Putin’s nuclear triggers poses an enduring threat to strategic stability. The potential for rapid and unintentional escalation remains present for Ukraine and its Western partners. The persistence of such uncertainty is essential to enabling Russian nuclear threats to deter challenges or—at a minimum—slow the pace of those challenges. In a world where the threat of nuclear use cannot be reduced to zero, the prospect of unwanted nuclear escalation will continue to enable Russia’s aggression against Ukraine.
The Kursk offensive has shown that Russia’s nuclear threats can be circumvented to some extent, helping Western policymakers recalibrate their estimations of the likelihood of nuclear escalation. These lessons are particularly relevant as Ukraine seeks permission to use Western supplied long-range munitions deep inside Russian territory with the apparent backing of some NATO countries, producing renewed threats regarding Russia’s red lines. The set of conditions under which Russia would use nuclear weapons to prevail in Ukraine appears to be narrow, but those conditions nevertheless exist as dangers of which policymakers must be mindful.
Giles David Arceneaux is the Rossetti Senior Research Fellow for Future Conflict at the United States Air Force Academy’s Institute for Future Conflict and an assistant professor of political science at the University of Colorado, Colorado Springs. The views expressed in this piece are those of the author and do not reflect the official policy or position of the US Air Force, the US Department of Defense, or the US government.