In 2025, the new Trump administration seems intent on transforming the U.S. security relationship with Europe. But would the loss of U.S. security guarantees also disrupt nonproliferation pledges by longstanding U.S. allies? High-profile speeches in Europe by Secretary of Defense Pete Hegseth and Vice President JD Vance, alongside the televised verbal confrontation of Trump and Vance with visiting Ukrainian President Volodymyr Zelenskyy, have triggered serious doubts as to whether the United States would come to Europe’s defense in the face of a threat from Russia. Allies in Australia, South Korea, Japan, and Taiwan have also expressed concern about growing U.S. retrenchment.
Extended security guarantees are costly, but academics, analysts, and policymakers have justified those costs by pointing out that allies might otherwise pursue their own nuclear weapons programs. As if to underscore this possible link between U.S. retrenchment and proliferation, on Friday, Polish Prime Minister Donald Tusk announced that Poland needed to embark on a large-scale military buildup that would necessitate reaching “for the most modern capabilities also related to nuclear weapons and modern unconventional weapons.”
U.S. military alliances and security guarantees in Europe and Asia since the Cold War involved a commitment to defend U.S. allies, including with nuclear weapons if needed. With those commitments fraying, will the danger of nuclear proliferation go up? To discuss today’s proliferation landscape, Good Authority editor Christopher Clary chatted with Nicholas Miller, an associate professor of government at Dartmouth College and author of Stopping the Bomb: The Sources and Effectiveness of US Nonproliferation Policy (Cornell University Press, 2018).
Christopher Clary: In your book and related articles, you argue that beginning in the 1970s the United States has had remarkable success at constraining nuclear proliferation. Why was that, in your view?
Nicholas Miller: In the early part of the Cold War, the United States did not prioritize preventing the spread of nuclear weapons. Instead, U.S. foreign policy focused overwhelmingly on competition with the Soviet Union and building a strong alliance bloc in that context. Washington did little to try to stop Britain or France from acquiring nuclear weapons and considered establishing a multilateral nuclear force in NATO that would be independent from U.S. control.
Beginning in the late 1960s, in large part due China’s first nuclear test in 1964, the United States decided to pursue a much more vigorous nonproliferation policy, including opposing proliferation by allies. In part this was because the Johnson administration concluded proliferation could not be contained to particular friendly countries. Allowing one country to acquire nuclear weapons would put pressure on other countries to follow suit. This change in thinking facilitated agreement with the Soviet Union on the 1968 Nuclear Nonproliferation Treaty.
The nonproliferation regime was strengthened in the 1970s when the U.S. Congress passed legislation mandating sanctions on proliferators, including cutoffs in economic and military aid and civilian nuclear assistance. This forced U.S. partners to make a choice: Maintain U.S. support or seek an independent nuclear arsenal. This threat of sanctions convinced South Korea and Taiwan to roll back their nuclear weapons programs in the 1970s. My research additionally suggests the threat of sanctions has helped deter U.S. partners from starting nuclear weapons programs since the late 1970s.
Given that context, how do you think about the prospects for continued nonproliferation success in this present environment?
The Trump administration’s attitude toward alliances is clearly causing some U.S. partners to reconsider their nuclear choices. That said, as long as the United States does not abrogate these security alliances outright, it still has tremendous leverage it could bring to bear. One big unanswered question is the extent to which the Trump administration views nonproliferation as an important policy goal. During the 2016 campaign, Trump made statements suggesting he was not concerned by allied proliferation. However, his first administration did not challenge the key tenets of U.S. nonproliferation policy.
If we assume a similar policy this time around, I expect some U.S. allies will move toward nuclear hedging, or enhance existing hedging postures. That would involve investing in civilian nuclear infrastructures and/or dual-capable delivery systems that would shorten the time it would take to build a nuclear arsenal – if that decision is taken down the road. Some allies may also explore alternative extended deterrence arrangements, as Germany appears to be with France. However, I would not expect crash programs to build nuclear weapons.
The nightmare scenario for proliferation would be the Trump administration signaling acceptance of allied acquisition of nuclear weapons – or fully abandoning key alliances. Either policy would effectively squander the leverage the U.S. has used historically to prevent widespread nuclear proliferation.
In one of your articles, you show that the U.S. intelligence community got better at predicting which governments were trying to build nuclear weapons over time. I know you are not in the intelligence community, but which country would you bet on developing nuclear weapons in the next decade?
While much of the focus at this moment is on U.S. allies, I still think the answer is Iran. Their facilities could produce highly enriched uranium for weapons within a matter of days and recent reporting suggests Iran may have revived its weaponization efforts. Trump claims to want a new nuclear deal with Iran. While a temporary freeze or slowdown in Iran’s nuclear program is not out of the question, particularly if Russia and China encourage Iran to do so, it’s unlikely Iran would trust the United States sufficiently to agree to a substantial rollback in its capabilities given the Trump administration’s prior withdrawal from the 2015 Joint Comprehensive Plan of Action (JCPOA).
When we combine this with Iran’s weakened security situation, involving both the degradation of its proxy forces and weaknesses exposed in its conventional missile forces, there are a lot of reasons to believe Iran might consider crossing the threshold in the coming years. This would be fraught with risks given the possibility of U.S. and/or Israeli military action, but I do not think we can rule it out.
