A Return to Nuclear Testing: Subcritical, Supercritical, or Weapons Test? 

Registration is now closed for this event page. Please note this conversation will be pre-recorded and aired on November 20, 2025 after 1:30 PM EST.

On October 29th, President Trump posted that the United States should restart nuclear testing “on an equal basis” with Russia and China. The statement was met with alarm and fears of a return to mushroom clouds and explosive weapons tests. It also raised concerning questions about what type of testing the president was referring to, and how the international community might respond to a return to nuclear testing. 

For years, U.S. government reports have raised concerns about Russian and Chinese compliance with a testing moratorium. These concerns are tied to supercritical testing, which might not produce a yield detectable by global seismic monitoring systems, but would nonetheless violate the "zero yield" interpretation of the moratorium and the Comprehensive Test Ban Treaty. Conversely, the United States has relied on subcritical testing for its Stockpile Stewardship Program. So should the United States match Russia and China by starting supercritical testing? To unpack these issues and more, please join Heather Williams, Director of the Project on Nuclear Issues and Senior Fellow in CSIS’s Defense and Security Department. 

This event is made possible through general support to CSIS.