On October 29, 2025, President Donald Trump announced that the United States will resume nuclear weapons testing, effectively ending a 33-year moratorium that has been in place since 1992. This declaration, made shortly before a scheduled meeting with Chinese President Xi Jinping, came via Trump’s social media platform, Truth Social, where he justified the decision by citing testing programs by other countries. He instructed the Pentagon—referred to as the “Department of War” in his statement—to begin testing U.S. nuclear weapons “on an equal basis.” This unexpected move has reignited debates about the technical, political, and strategic implications of restarting nuclear tests.
The last U.S. nuclear test was conducted underground at the Nevada Test Site in 1992, marking the symbolic end of the Cold War nuclear arms race. Over several decades, the U.S. had carried out more than 1,000 nuclear detonations, a vast body of testing that has provided detailed data for maintaining and modernizing the country’s nuclear arsenal. The civilian Department of Energy, which oversees the U.S. nuclear stockpile, has since relied on subcritical tests—experiments that do not produce a nuclear yield—to monitor weapon reliability. These tests involve small-scale laboratory experiments performed deep underground, which avoid the political and environmental consequences of full-scale detonations.
Trump’s announcement echoes recommendations made in the “Project 2025” report, a policy document aligned with his administration’s strategic goals. The report advocates for resuming underground nuclear tests to ensure the effectiveness of the nuclear stockpile. Trump’s decision also follows recent demonstrations by Russia of novel nuclear-capable weapons, including a nuclear-powered cruise missile and an underwater drone capable of carrying nuclear warheads. Although Russia and China have not conducted nuclear detonations in recent years, both countries remain signatories to the Comprehensive Nuclear-Test-Ban Treaty (CTBT)—a treaty that bans all nuclear explosions but which the U.S. has signed but never ratified. China has also not ratified the treaty, and notably, Russia formally withdrew its ratification in 2023. The last nuclear test conducted by China was in 1996, and the Soviet Union’s last test was in 1990. Both Beijing and Moscow have expressed concern over Trump’s announcement, and Russia has even threatened to resume its own nuclear tests in response.
To better understand the ramifications of this decision, Scientific American interviewed Jeffrey Lewis, a leading expert on nuclear geopolitics at the James Martin Center for Nonproliferation Studies at the Middlebury Institute of International Studies. Lewis provided critical insights into the technical and political aspects of resuming nuclear testing and the broader impact it could have on global nonproliferation efforts.
Lewis began by addressing the technical rationale behind resuming nuclear tests. He emphasized that the U.S. currently has extensive capability to test nuclear weapons in numerous ways short of full-yield detonations. The existing subcritical tests carried out beneath the Nevada desert provide data without producing a nuclear explosion. He pointed out that it remains unclear what kind of testing Trump envisions—whether it involves full-yield underground detonations or smaller-scale experiments with limited yields. Each type of test serves different technical purposes.
Crucially, Lewis argued that there are no meaningful technical benefits to resuming full-yield nuclear testing. The U.S. already possesses a vast amount of data from over a thousand past tests and has developed highly sophisticated computer models to simulate nuclear detonations and weapon performance. Modern science and technology have improved understanding of nuclear weapons beyond what was possible during the era of active testing. Lewis contended that the only countries that stand to gain new knowledge if nuclear testing resumes are Russia and, to a larger extent, China, which have less extensive testing histories and resources.
Regarding the specific call in the Project 2025 report to resume underground nuclear tests, Lewis noted that during Trump’s previous administration, officials had discussed restarting nuclear testing but realized it would take years to prepare. There was also talk of conducting “uninstrumented” tests—detonations without data collection instrumentation—which Lewis described as pointless demonstrations of capability rather than meaningful scientific experiments. Such tests would only serve to prove that nuclear weapons still function but would offer no new technical information to guide arsenal maintenance or modernization.
Lewis then turned to the broader international consequences of breaking the nuclear testing moratorium. Resuming nuclear tests could potentially collapse the global test ban regime, undermining decades of efforts to prevent nuclear proliferation