In an open letter posted on Medium on Thursday, Christopher Ford, former Assistant Secretary for International Security and Nonproliferation, said he intervened to prevent the US government from “embarrassing and discrediting” itself by accusing China of having deliberately engineered the coronavirus — despite there being no evidence to make that case. In an interview with BuzzFeed News, Ford said his colleagues were pushing to include allegations that China had breached the international Biological Weapons Convention in a State Department report to Congress, which could have set off a diplomatic crisis with one of the US’s chief global rivals. It is highly unusual for a former senior State Department official to publish a personal account of recent internal disputes. But Ford’s open letter comes in the midst of an acrimonious debate over the so-called “lab leak” hypothesis for the emergence of COVID-19. The most extreme version of this theory suggests that Chinese scientists engineered SARS-CoV-2 as a bioweapon.