By examining via a case study the political authority of US proliferation experts since the 1960s, this article contributes to nuclear weapons proliferation studies and to the growing literature on the role of expertise in democracies. First, it argues that policy choices are determined by an understanding of history and that approaching nuclear history as a history of nuclear weapons proliferation is a presumption shared by both US experts and policy makers. Second, it shows that this understanding of history, relying on the metaphorical use of the term proliferation (which was imported from biology), strongly distorts the facts. Third, the article shows that nuclear experts are plagued by a conservative bias as a result of this use of the proliferation metaphor. Instead of challenging the faulty proliferation narrative, most experts have backed it without question. Fourth, the legitimacy that experts lend to this view of history has important political effects: it provides an authoritative assessment of past policies and limits the possibility of political innovation. Policy initiatives tend to be restricted to changes in speed or intensity. The article suggests three changes that might restore room for informed political innovation in nuclear weapons policies.