Four years later, insights from the probe into the attempted assassination of defector Sergei Skripal in Salisbury, England, are helping to fuel worries that Russian chemical weapons could soon turn up in yet another country, with far graver consequences. The Biden administration has repeatedly warned that Russia, frustrated with the faltering progress of its 3-week-old invasion of Ukraine, may be preparing to use chemical weapons against Ukrainian troops, political leaders or even ordinary civilians in an effort to regain momentum and seize control of key cities.

While the nature of those preparations is not publicly known, current and former U.S. and NATO officials say Russia has long possessed an array of chemical weapons, which it retains in defiance of international treaties and despite years of Russian promises and pronouncements. Moreover, senior Russian leaders appear to regard chemical weapons as a legitimate tool for achieving a variety of goals, from eliminating political foes to subduing armed opponents, officials and weapons experts say. Russia denies possessing chemical weapons, and the Kremlin has accused Kyiv and Washington of plotting to use chemical or biological weapons in Ukraine…

“The Skripal case was the smoking gun,” said Andrew C. Weber, a top nonproliferation official for the Pentagon during the Obama administration and an expert on Russia’s weapons of mass destruction programs. “Russia used chemical weapons, in peacetime, in a foreign country. The thought that they might now use chemical weapons in Ukraine is entirely rational.”