Memo to the president: How to deter Russian nuclear use in Ukraine—and respond if deterrence fails

What does the US President need to know? Our new Memo to the President series has the answer, with briefings on the world’s most pressing issues from our experts, drawing on their experience advising the highest levels of government.

Conclusion in advance: Russia could use nuclear weapons to achieve its goals in the war in Ukraine – a risk that has only grown as Russian forces confront Ukrainian counter-offensives. Such nuclear exploitation could advance the Kremlin’s military goals, undermine US interests worldwide, and unleash a humanitarian catastrophe not seen since 1945. To deter such a potential catastrophe, the United States should publicly and deliberately vaguely threaten grave consequences for any Russian use of nuclear weapons and stand ready to launch conventional military strikes against Russian forces if deterrence fails.

Background: The Russian nuclear use in Ukraine is possible and would harm US interests

After Russia’s continued incursion into Ukraine this year, the United States and its allies and partners have responded with military aid to Ukraine, sanctions on Russia’s economy and reinforcements of NATO’s eastern flank. So far, the US and its allies have ruled out direct military intervention against Russia.

Nuclear threats are at the heart of Russian military strategy, and there is a non-zero probability that Russian President Vladimir Putin will order a nuclear strike against Ukraine.

• Russia’s so-called “escalation-to-de-escalation” strategy calls for nuclear threats and, if necessary, limited use of nuclear weapons to force an end to the conflict on terms favorable to Moscow.
• Putin has issued a series of nuclear threats against the United States and the West in order to prevent them from coming to Ukraine’s defense.
• In addition, Russia has used dual-capable weapons (capable of carrying both nuclear and conventional warheads) against Ukraine and has conducted exercises with its nuclear forces.
• Putin may believe he could use nuclear weapons to force the United States and the West to stop supporting Ukraine.
• Russia has a wide range of options for conducting non-strategic nuclear attacks, using one or more of the thousands of low-yield nuclear weapons it already possesses. Russia could use such nuclear weapons on a limited basis against Ukrainian forces, bases, logistics centers and even cities.

Russia’s nuclear use would harm US interests in the war in Ukraine and around the world.

• Such a strike could cause a humanitarian catastrophe, deal a crippling blow to the Ukrainian military, split the Western alliance and force Kyiv to sue for peace.
• It would also break a nearly eight-decade-old taboo on the use of nuclear weapons. It may increase the likelihood of future use of nuclear weapons when states (e.g., China) recognize that nuclear weapons can help them achieve their goals without serious military retaliation from the United States and its allies. In addition, it could lead to nuclear proliferation if states fear nuclear weapons could be used against them, or if US allies believe Washington will not respond to a nuclear attack.

Recommendations for US policy to prevent Russian nuclear use

To prevent Russia from using nuclear weapons in Ukraine, the United States should issue a clearer deterrent threat. It could choose between vague or explicit threats, made publicly or privately.

• For now, Putin may believe he could use nuclear weapons without any significant Western response. A stronger US deterrence threat would help dissuade him from that notion.
• A vague threat (e.g., “Russia’s decision to use nuclear weapons in Ukraine would risk the most severe consequences possible”) has the benefit of conveying to Russia that there would be nuclear deployment implications without directing the United States to a specific course of action to set.
• A more specific threat (e.g., “It is the policy of this nation to treat any nuclear attack on Ukraine as an attack on the United States requiring a full retaliatory response”) would have greater deterrent value, but would reduce the flexibility of the Restrict USA.
• While a vague threat might be dismissed as cheap talk, a more specific threat runs the risk of drawing a “red line” that Washington can’t enforce, making a vague threat the better option.
• These threats could be delivered privately, but a public threat would probably be more effective in deterring Russia and convincing allies, since US credibility with the world would be at stake.

Recommendations for a US Response to the Russian Nuclear Deployment

A more blatant threat should be enough to deter a Russian nuclear attack, but Washington must be ready to carry out its threat if deterrence fails.

retaliation option 1: The United States could step up its current approach: tightening sanctions on Russia, further isolating Moscow internationally, arming Ukraine with more advanced weapons, and redoubling efforts to militarily strengthen Eastern Europe.

• Russia’s nuclear use could offer an opportunity to persuade previously reluctant countries – like India and possibly even China – to participate in escalating sanctions.
• The United States could provide Ukraine with more advanced weapons to penetrate deeper into Russian territory and help Ukrainian units operate in a nuclear environment. This may include the provision of iodine tablets, radiation suits, Geiger counters and other relevant material.
• The United States and NATO could bolster their military presence in Eastern Europe by adding heavier and more durable conventional forces while moving US nuclear weapons to Poland. They could announce the development of additional types of low-yield nuclear weapons for use in Europe, such as B. a nuclear Joint Air-to-Surface Standoff Missile (JASSM) or a Ground Launch Missile (GLCM).
• The United States could go on nuclear alert to deter attacks on NATO allies. This could include visible steps to plant warheads on bombers and send nuclear submarines to sea.

advantages: These steps would impose costs on Russia, and Washington could plausibly claim that it has carried out its chilling threat.

Disadvantages: There is a risk that many friends and foes will view these measures as an inadequate response to a nuclear attack.

retaliation option 2: The United States could respond with military force.

• Possibility 2A: The United States could launch a limited conventional strike against Russian forces or bases directly involved in the attack. A more robust version of this option would be to join the war on the Ukraine side.

Advantages: Direct US military intervention would be widely perceived as a sensible response, potentially restoring Ukraine’s nuclear deterrent and reinforcing the global nuclear taboo.

Disadvantages: A military response increases the risk of escalation into outright war between Russia and NATO. Russia may conclude that the United States is unwilling to use nuclear weapons and encourage more Russian nuclear attacks. Some US allies might still see a conventional response to a nuclear attack as inadequate.

• Possibility 2B: The United States could use nuclear weapons to respond to and deter another Russian nuclear attack in Ukraine.

Advantages: A nuclear response will most likely increase deterrence of adversaries, reassure allies, and restore the global taboo against future use of nuclear weapons by demonstrating that countries cannot use nuclear weapons without dire consequences. Both allies and adversaries could be surprised or feel weak if the United States does not respond promptly to a nuclear attack on Ukraine.

Disadvantages: A US decision to use nuclear weapons would raise the difficult question of which Russian target to hit with which US nuclear weapon. A US nuclear strike could restore deterrence, but it could also provoke Russian nuclear retaliation, increasing the risk of a major nuclear exchange and another humanitarian catastrophe.

Given the above costs and benefits, if deterrence fails, the best US response might be a mix of Options 1 and 2A: an intensification of ongoing efforts to counter Russian aggression in Ukraine and a limited conventional strike against Russian forces or bases that have launched the nuclear attack.

---

Matthew Kroenig is Acting Director of the Council’s Scowcroft Center for Strategy and Security. He previously served in the Department of Defense and in the intelligence agencies of the Bush, Obama and Trump administrations, including the Offices of Strategy, Middle East and Nuclear and Missile Defense in the Office of the Secretary of Defense and the Strategic Office of the Central Intelligence Agency Assessment Group.