On October 30, President Trump, aboard a helicopter taking him to a meeting with Chinese leader Xi Jinping in Busan, South Korea, posted on Truth Social: “Because of other countries’ testing programs, I have instructed the Department of War to start testing our Nuclear Weapons on an equal basis. That process will begin immediately.” At the time, it was unclear why the president was re-examining the US commitment to a moratorium on nuclear testing that has been in place since 1992 and what sort of testing would be resumed. Subsequent events have clarified the administration’s intention to conduct nuclear tests comparable to assessments of testing in Russia and China, but the outlook for US testing remains unclear.
The moratorium
The United States declared a moratorium on nuclear testing after its last test, named “Divider,” which took place 1,400 feet beneath the Nevada desert in September 1992. President Clinton subsequently signed the Comprehensive Nuclear-Test-Ban Treaty (CTBT) in September 1996. While the United States has not ratified the treaty and it has not entered into force, the United States has maintained its commitment to a moratorium on nuclear testing.
The United States relies on a science-based Stockpile Stewardship Program to ensure the safety, security, reliability, and effectiveness of its nuclear weapons without the need for nuclear-explosion testing. As part of this program, experiments are conducted at the Nevada National Security Site that do not achieve criticality. These “subcritical” experiments do not result in a self-sustaining chain reaction that produces nuclear yield and are often called “zero yield” experiments. Under the moratorium, the United States refrains from nuclear activities that are supercritical—that exceed the zero-yield standard.
The United States is transparent about its nuclear activities. Officials of foreign governments and civilian experts have been invited to visit the facilities in Nevada involved with the Stockpile Stewardship Program, which relies on specialized analytical facilities and subcritical experiments.
Russia and China: intentions uncertain
Russia and China each declared a moratorium on nuclear testing after their last nuclear explosive tests in 1990 and 1996, respectively. Both countries state that they are observing a moratorium on nuclear testing without specifying what they consider to be nuclear tests and without referring to zero yield or any other standard.
There is considerable uncertainty about what activities are being pursued by Russia at its test site at Novaya Zemlya and by China at its site at Lop Nur. The US State Department, in its annual report on compliance with agreements and commitments, has stated for many years that some of Russia’s activities “have demonstrated a failure to adhere to the zero-yield standard, which would prohibit supercritical nuclear tests.” This continues to be the US government’s assessment of testing by Russia.
For many years, the State Department compliance report has stated that “concerns remain about activities at the Lop Nur Nuclear Test Site given the PRC’s lack of transparency on its nuclear testing activities at the site, its previous use of explosive containment chambers, and prior questions regarding its adherence to the ‘zero-yield’ standard in its nuclear weapons testing moratorium.”
The latest compliance report, issued in April 2025, stated that “no new adherence issues related to nuclear testing moratoria were identified” and referred readers to previous years’ reports for the more detailed assessments of activities at test sites in Russia and China quoted above. On February 6 of this year, however, Undersecretary of State Thomas DiNanno revealed a new public assessment that China had conducted yield-producing nuclear tests, including one on June 22, 2020. On February 17, Assistant Secretary of State Christopher Yeaw elaborated that the June 2020 event was detected at a seismic station in Kazakhstan with a magnitude of 2.75. Yeaw said “there is very little possibility” that the event “is anything but an explosion” and added that the data were not consistent with mining blasts or an earthquake. “It is . . . what you would expect with a nuclear explosive test,” he said.
Later that day Robert Floyd, executive secretary of the Comprehensive Nuclear-Test-Ban Treaty Organization, which oversees the monitoring station in Kazakhstan, issued a statement that the monitoring system had detected two very small seismic events on June 22, 2020. He stated that these events were far below the level at which the system is currently capable of identifying events consistent with nuclear test explosions, and as a result, with these data alone, it is not possible to assess the cause of these events with confidence. The accounts by Yeaw and Floyd are not necessarily inconsistent; Yeaw may have access to additional information.
What could Russia and China learn?
The 2012 report of the National Research Council (NRC) of the National Academies of Sciences, Engineering, and Medicine on technical issues related to the CTBT found that “based on Russia’s extensive history of hydronuclear [a synonym for “supercritical”] testing, such tests could be of some benefit to Russia in maintaining or modernizing its nuclear stockpile. However, it is unlikely that hydronuclear tests would enable Russia to develop new strategic capabilities outside of its nuclear-explosion test experience.”
The NRC report did not make a specific finding for the potential benefit of supercritical tests for China. Such tests could also be of some benefit to China in maintaining or modernizing its nuclear stockpile. The nuclear explosion test experience for China (45 nuclear explosive tests prior to the moratorium) is much smaller than for Russia (715) and the United States (1,030).
The NRC report does not find a similar potential benefit for supercritical tests by the United States: “Hydronuclear tests would be of limited value in maintaining the United States nuclear weapon stockpile in comparison with the advanced tools of the Stockpile Stewardship Program.”
What could the US investigate?
Since President Trump posted on Truth Social that because of other countries’ testing programs he had directed testing of US nuclear weapons “on an equal basis,” administration officials have described the parity concerns as motivating this change in the US approach. But it is still unclear what size tests the United States would pursue.
In an interview three days after Trump’s post, Energy Secretary Chris Wright said that “these are not nuclear explosions,” suggesting that the United States would not be resuming large-scale nuclear explosive tests. A US official in Vienna (headquarters of the Comprehensive Nuclear-Test-Ban Treaty Organization), subsequently said, “As President Trump indicated, the United States will begin testing activities on an equal basis with other nuclear-armed states,” suggesting that the United States would conduct tests with yields up to those demonstrated by Russia and China. In his February 5 statement, DiNanno added that “the president was referring to Russian and Chinese nuclear testing in violation of their respective moratoria on yield-producing nuclear tests,” again suggesting that US tests would be comparable to those of Russia and China.
These statements suggest that in calling for testing “on an equal basis,” the Trump administration is seeking to establish reciprocity with Russia and China by moving to conduct tests comparable to theirs. The administration’s assessment of the yields of Russian and Chinese tests, however, is not clear. If the administration concluded that Russia and China are conducting supercritical tests, that would imply that the United States would proceed with its own supercritical tests, which could have nuclear yields up to perhaps the equivalent of two kilograms of TNT.
If the June 2020 Chinese test becomes the benchmark for future US tests, however, the situation would be more complex. The magnitude 2.75 seismic signal detected for the June 2020 test would correspond to a yield of about twenty tons if it were caused by a nuclear explosion under standard testing practices, according to the 2012 NRC report. In a February 23 statement to the UN Conference on Disarmament, Yeaw said the estimated yield was ten tons, assuming standard test practices, or higher if China took steps to diminish the seismic signal. This suggests that the administration may propose testing by the United States with yields of ten tons or more, depending on its assessment of the Chinese test.
The 2012 NRC report found that testing with yields between one and one hundred tons would allow the United States, Russia, and China to partially validate design codes, modernize their arsenals, and develop low-yield weapons. The report found that they are unlikely, however, to be able to deploy new types of strategic nuclear weapons that fall outside the design range of their nuclear-explosion test experience without several much larger (multi-kiloton) tests.
Potential consequences
Russian President Vladimir Putin has said that if the United States or another CTBT signatory were to conduct a nuclear test, Russia would take reciprocal measures. China and some other states with nuclear weapons would also likely reassess their nuclear testing policies, and it is hard to predict the ultimate outcome for future restraint on nuclear testing. Such a setback would likely have serious consequences for nuclear nonproliferation. Resumption of nuclear testing would also begin to erode the advantage the United States enjoys by having more nuclear testing experience than any other country.
By law, the directors of the three nuclear weapons laboratories and the commander of the US Strategic Command are required to make annual assessments of the safety, reliability, performance, and military effectiveness of US nuclear weapons, including determinations of the potential utility of nuclear testing to resolve issues. These classified assessments are provided to the president and Congress, and they underpin the Stockpile Stewardship Program to ensure the US strategic deterrent is safe, secure, and effective without nuclear explosive testing. No US official has argued that the United States needs to resume nuclear testing for technical reasons. The argument has been based entirely on a need for equality and reciprocity.
An alternative approach to equality and reciprocity in nuclear testing would be to increase transparency into nuclear testing activities. In June 2023, the administrator of the National Nuclear Security Administration said the United States was open to working with others to develop a regime that would allow reciprocal observation with radiation-detection equipment at each other’s subcritical experiments to allow confirmation that the experiments are consistent with the CTBT. Such transparency would enable a move toward reciprocity in which the United States, Russia, and China would all forgo tests above zero yield, rather than reciprocity in testing above the zero-yield threshold. Such an outcome would support nonproliferation of nuclear weapons and help preserve the enduring advantage the United States holds, thanks to having more nuclear testing experience than any other country.
