The Nuclear Implications of Trump’s plan to End the Ukraine War

A snapshot into the possible increased reliance on nuclear weapons in Europe, and increased risks of friendly proliferation (disclaimer, who knows what happens tomorrow).

B61-12 nuclear gravity bomb in the weapons bay of an F-35A. Courtesy of r/WarplanePorn.

Following a flurry of information from the Trump Administration today, we (yes, co-authorship, send negative feedback directly to Vipin) thought it would be useful to highlight two understated, but important, nuclear issues that arise from the U.S. approach. Bottom line, the reduced U.S. commitment to European security stemming from the Administration’s announced approach (which shouldn't surprise observers of the President’s campaign and statements by many of his closest advisors) may create a greater P3 reliance on nuclear weapons to maintain regional deterrence in Europe, increase the risk that Ukraine proliferates, and consequently, could bring Europe closer to another nuclear crisis with Russia in the near future.

(Note: Perhaps this disclaimer goes without saying, but information regarding President Trump’s approach to Ukraine is subject to change. There is a fair amount of unpredictability regarding the Administration’s positions, as we’ve already seen indications of a walk back from Secretary Hegseth today. That being said, hopefully this post offers readers a sense of the important nuclear dynamics connected to shifts in America’s approach to Ukraine, Europe, and Russia.)

The New Ukraine Baseline

Between President Trump’s comments on Truth Social and in the Oval, and Secretary of Defense Hegseth’s statement at yesterday’s Ukraine Defense Contact Group, the Administration conveyed elements of its approach to ending the Ukraine war. Here are the core aspects:

1. Soon, the US will begin negotiations with Russia to end the Ukraine War, and Ukraine (and other European countries) may not be in attendance;

2. Ukraine will not join NATO;

3. The responsibility for Ukraine’s defense after the conflict will be left to Ukraine and European supporters. Any defense or “peacekeeping” mission that involves Allied troops will not be a “NATO mission”—the Art. V backstop will be explicitly absent;

4. Europe will take on the burden of security assistance to Ukraine to help it stand up it's military, implying U.S. aid will not be guaranteed (though President a Trump previously discussed trading arms for rare earth minerals and its likely a topic Vice President Vance and President Zelenskyy will discuss shortly in Munich); and,

5. Alongside these steps, the US may reduce its military footprint in Europe as part of an unambiguous shift in attention to deterring the PRC, per Hegseth's comments regarding a “division of labor” and the “realities” of threats facing the United States in Asia and the border.

The elements of Trump's plan for Ukraine represent a clear departure from the previous U.S. position, where NATO membership for Ukraine remained a (contested) possibility, a range of countries including the United States made bilateral security assurances to Kyiv in addition to a multilateral compact to support Ukraine’s long term security. If the United States—to this point Ukraine’s largest individual backer for defense articles and financial support—were to back out of these prior commitments, European allies and Ukraine face a deterrence vacuum to fill without quick and easy solutions. Given Russia’s predations on Europe under the shadow of its nuclear arsenal, this creates two nuclear dilemmas.

Pressure to Increase Reliance on Nuclear Deterrence

First, a reduction in overall conventional strength in Europe may create allied demands to increase reliance on nuclear weapons to preserve regional deterrence. European allies who were slowly building up defense strength, including their industrial bases to support rearmament, will now need to do so with diminished US conventional support. The near-term inadequacy of NATO’s conventional deterrent, considered an area of advantage against Russia with status quo ante US involvement, creates more incentive for Russia to test Europe militarily.

Russia long relied on a large NSNW arsenal and some subtle (and more recently, not so subtle) nuclear threats to overcome a clear comparative deficiency in conventional capabilities. Facing a nuclear disadvantage, and perhaps losing a conventional advantage without a sizeable U.S. military presence, NATO may face more aggressive provocations from Russia than the “grey zone” cyber, undersea, and sabotage operations observed in the past few years. While NATO Allies will try to scramble to bolster defense capabilities at a greater pace, they will certainly view the method by which the Trump Administration conveyed the new normal as deeply disturbing. Nothing in today's announcements suggested the United States has thought through how to make up the resultant assurance deficit, one which may force some European countries to consider concessions to ease tensions with Russia, while others decide to arm up – an unwelcome break in what has been a remarkable record of European cohesion throughout the conflict.

One approach to bolstering regional deterrence could entail increasing reliance on nuclear capabilities. This could take either or both of two forms.

Form One: The United States could enhance it's existing extended deterrence commitments to NATO. The size of the US arsenal and availability of forward deployable nuclear weapons such as the B61 and a modern delivery platform in the F-35A offer options to increase the existing NATO nuclear deterrent. The United States could also ask other allies to join the NATO nuclear mission, expanding participation to include other allies who operate F-35As not yet certified for nuclear missions, but perhaps will be open to doing so in an environment where the U.S. military footprint in Europe is diminished. However, it's possible European allies will look for an even greater US nuclear commitment to Europe, in the form of additional B61s, F-35s, a transparent allocation of U.S. strategic weapons to Europe, or a new forward-deployed, regional nuclear capability. However, applying U.S. nuclear salve to an open assurance wound is not free, even if cheaper than maintaining a larger conventional presence, and to the extent the Trump Administration's moves on Ukraine are designed to do the opposite—reduce U.S. defense commitments to the region to save costs.

Form Two: The UK and France could formalize agreements to extend nuclear deterrence to European allies, and potentially Ukraine as well. This approach would fit the U.S. goal of Europe taking care of its own, but comes with clear negatives. The UK and French arsenals are small compared to Russia, each designed to enable relatively restrained nuclear strategies based on threatening massive retaliation to deter Russian strategic attacks. The UK formally extends its deterrent to NATO Allies, and France does not and its deterrent is designed against Russian threats to French territory, though French President Macron has openly mused about a “Euro deterrent” approach without specifying exactly what that would look like. The lack of flexibility inherent in UK and French nuclear arsenals do not present a credible deterrent to Russian conventional aggression or limited nuclear use against other allies. It's possible the UK or France could change nuclear doctrine, posture, and capabilities, but these actions would take significant time and resources far beyond current, ongoing nuclear modernization efforts - far more daunting than the immediacy of the coming challenges to European security will allow.

The main problem with either approach is that convincing Russia, with thousands of NSNW, that an enhanced regional nuclear deterrent is credible, is difficult to do without strong conventional forces. U.S./NATO strategy in Europe for decades has relied upon fielding strong conventional forces along with forward deployed nuclear forces - nuclear capabilities helped manage uncertainty regarding the credibility of conventional forces, and conventional forces helped manage the risk that limited nuclear war was uncontrollable, and thereby deterrence by threatening limited nuclear use was not credible.

Regardless, European allies will consider the politics - and popular opinion - of the US approach first and foremost. Throughout history, US nuclear umbrella allies made nervous by fading or changing US commitments or other changes in their security outlooks have sought increased deterrence. In the nuclear context, many allies sought firmer US commitments to extended deterrence during consultations for the last two Trump and Biden NPRs. In the most worrisome crises, some allies have more favorably considered developing their own nuclear weapons.

The Pendulum Swings Toward Proliferation

A second concern arising from the Administration's position is the (edit: probably low) possibility that Ukraine pursues a nuclear weapon. Perhaps lost in the coverage of Trump and Hegseth statements is Volodymyr Zelenskyy’s comments last week, wherein he repeated an earlier demand that Ukraine needs NATO guarantees or a nuclear deterrent. Clearly, with NATO membership off the table, attention may turn to an indigenous nuclear weapons program.

There are various examples of near-miss nuclear proliferation throughout history, and none are perfect analogues to the current Ukraine discussion. However, it's worth considering Taiwan's experience in the Cold War. At various points since the Communist Party took control of China, Taiwan flirted with a nuclear weapons program, feeling pressure a few particularly worrisome moments for Taipei. Several key moments pushed Taipei to pursue a latent nuclear weapons capability: the PRC’s test of a nuclear weapon in 1964, Nixon's rapprochement to Beijing in the 1970s, ending defense commitments to Taiwan and removing nuclear weapons from Taiwan, and Taipei’s loss of diplomatic recognition internationally and in the UN system. The geopolitical trends for Taiwan, and crisis of confidence faced by Taipei’s leaders with the world's pursuit of diplomatic relations with mainland China, led to two decades of quiet pursuit of nuclear latency.

Ukraine’s pursuit of a weapon would be very different. It's unlikely Ukraine would be able to hide its development, and would be under immediate and constant threat of Russian attack. Immediately, nations would probably condemn Ukraine if and when the information regarding its nuclear program became public, reducing support across Europe for assistance to Ukraine and leaving Kyiv even more vulnerable to Russia. In the worst case, Russia returns to its 2022 dirty bomb playbook and views Ukrainian proliferation as pretext for its own nuclear use. It is also unlikely European powers could commit to militarily defending Ukraine’s pursuit of the bomb outside of its NPT obligations, risking their own territory to Russian attack while Ukraine’s weapons program is vulnerable for a period of years.

Ukraine’s pursuit of a bomb would create an immediate regional crisis, one caused by the absence of US leadership and unlikely to be safely resolved for the same reason. It's hard to imagine the Trump administration completely ignoring this event were it to occur in its watch, though they may be hoping to punt such a crisis to a future administration, creating another latent nuclear proliferation problem in the world that in the best case could remain on the back burner.

Despite the costs associated with proliferation, Kyiv may feel it has no other choice. As evidenced by the Taiwan example, a security dilemma where territorial integrity is at daily risk is existential in nature for smaller countries facing larger, nuclear armed foes creates high pressure for nuclear proliferation. The failure of the United States to avoid creating a scenario where there is no other way out will be to blame.

What to Look for in the Coming Days

The nuclear implications of the Administration’s approach to the Ukraine conflict are largely tied to broader political and military considerations of U.S. security guarantees to European allies, the allies faith in the United States, and the actual-vs.-perceived needs of shifting overall U.S. defense posture towards the Indo-Pacific. The statements made by President Trump and Secretary of Defense Hegseth point toward a forewarned shift in focus and capabilities from Europe to Asia; this brings up questions regarding the fate of Ukraine, but also huge concerns regarding the viability of the U.S. nuclear guarantees to its treaty allies.

However, the worst case scenario is not inevitable. In the coming days, it will be important for the Administration to answer several questions. Here are three that are important to the authors:

How is Trump thinking about US extended nuclear deterrence policy alongside the Ukraine conversation? Is the United States willing to do more to improve extended deterrence software and hardware in conjunction with following through on its Ukraine plan?

OK, there is some logic to strengthening reliance on nuclear capabilities in Europe if the United States is going to remove conventional and other capabilities. A nuclear security blanket for NATO that could allow Allies to concentrate more of their defense expenditures and conventional capabilities on supporting Ukraine (of course, there are also risks that come with this approach vis a vis escalating tensions with Russia). However, based on Hegseth’s comments today, it's hard to see how the United States will both increase its nuclear presence or posturing in Europe if the only adversary of concern is China. That could provide some much needed leverage in coming talks with Russia; the statements yesterday seemed to offer Russia more than it asked for in the 2022 Istanbul Communique.

Will the Trump Administration conduct new arms control talks in parallel with Russia and China (or at least run a semi Reagan-esque nuclear zero play with the hopes of blaming Moscow and Beijing for refusing to engage), with the potential to reduce nuclear risks to Ukraine and European allies through diplomacy?

Today, Trump proposed starting nuclear arms talks with Russia and China with the aim of all three countries cutting spending on nuclear weapons, and “spending on other things that are actually, hopefully, much more productive,” while suggesting he will ask Putin and Xi to “cut our military budget[s] in half.”

Readers will recall the Trump Administration’s attempts at trilateral arms control negotiations in 2019-2020, which China was unwilling to join. The process moved toward bilateral U.S.-Russia talks designed to replace the New START Treaty, which was due to expire in 2021, with the U.S. aiming to cover all Russian nuclear weapons under some numerical limits, including the large non-strategic nuclear weapons stockpile that poses the most direct threat to Europe (as Ambassador Marshall Billingslea put it at the time:

President Trump offered President Putin the opportunity to do something that none of his predecessors were willing or able to do: put a cap on both countries’ nuclear stockpiles, covering all nuclear warheads.

That process ran out of time, and President Biden came into office and extended New START for five years.

In the near future, we’ll post something on the various arms control approaches the administration could take with Russia and China; without spoiling that coming attraction, there are a number of reasons why trilateral arms control will be extremely difficult. However, for the sake of European allies and to regain some lost leverage regarding Ukraine, Trump should consider making substantial demands on Russia related to nuclear weapons, linking progress on Russia’s political asks related to Ukraine to substantially reducing Russia’s nuclear threat to Ukraine and Europe in a Kissingerian approach that some of his close advisors may have a fondness for.

Let’s recall that one of the many reasons President Trump used to rationalize his support for a rapid exit from assisting Ukraine was the constant specter of Russian nuclear use, stating “I will prevent, I promise, World War III. And we are very close to World War III,” in December 2024.

Will the Administration support, ignore, or discourage allied proliferation?

The United States has successfully managed the risks of allied proliferation in the past. However, these efforts have often come at the expense of greater commitments to conventional force posture, enhancing allied defense capabilities, and ensuring the credibility of extended nuclear deterrence commitments to bolster allies confidence in managing crises on their own.

Incoming Trump advisers like Elbridge Colby have suggested they don’t really care whether U.S. allies proliferate to defend themselves—if we want those allies to do more from themselves we can’t restrain them, so the thinking goes. Such an approach would overturn decades of U.S. nonproliferation policy, focused on preventing any proliferation by anyone. However, pro-proliferation proponents are correct in noting that U.S. extended deterrence to avoid new nuclear states can be expensive. The cost has always been worth it to the United States throughout the Cold War.

In some cases, U.S. presidents placed significant diplomatic, economic, and military pressure on a potential friendly proliferator to turn off nuclear ambitions. The initial steps taken by the Trump administration point to an increased risk of Ukraine pursuing a nuclear weapon, if the remaining elements of the administration's strategy aren't cobbled together quickly. Having a plan to discourage, with a coalition of other countries that support the nonproliferation regime, will be important. The plan should not only include sticks, either, but carrots in the form of assistance or assurance. More to follow on this topic as well.

We suspect the statements made yesterday will lead to a pretty intense next few days around the Munich Security Conference, and more Administration views will trickle out into the public space. Hopefully, a plan to mitigate nuclear risks as part of the approach to winding down the Ukraine conflict will be part of the next exposition. Until then, feel free to reach out to us with questions/comments.