From conspiracy theory movement to challenger party: why the case of Japan’s Sanseito isn’t more widely replicated

Why has the recent rise in the salience of conspiracy theory beliefs not led to a matching rise in challenger parties strategically embracing such beliefs? The increase in participation in online conspiracy theory communities in many countries has been fuelled by a general rise in affective polarisation as well as by specific events such as the COVID-19 pandemic. As these conspiracy-focused communities have grown, some media outlets and political parties have begun to echo conspiracy theory rhetoric, using "dog whistle" strategies to reference conspiracy narratives and thus appeal to these groups. While many citizens strongly reject conspiracy narratives, they appeal to a minority who also tend to be highly dissatisfied with the existing political establishment. In theory, this creates an opportunity for new challenger parties to stake out issue ownership over these narratives. However, in practice new challenger parties which openly embrace conspiracy theories in an effort to capitalise on the recent high profile of such narratives are very rare. This paper examines the case of Japan’s Sanseito ("The Party of DIY"), an explicitly conspiracy theory focused party which was founded in 2020 and won its first seat in the national Diet in 2022. The Sanseito’s emergence and its organisational strategies are the product of a political and social context which shares many features with other developed nations, including declining trust, the Balkanisation of online media spaces, and anger among some groups at perceived government overreach in pandemic-era policies. However, there are also some unique features that help to explain why similar parties have not emerged elsewhere. Among those are Japan’s Upper House electoral system, which makes it relatively easy for fringe parties to win seats – similar to the electoral system in the Netherlands, where we find arguably the only comparable "conspiracy theory party", PvD ("Party for Democracy"). We argue that another key factor is the degree to which major political parties are constrained from engaging with conspiracy narratives. While major parties in countries including the USA and UK have engaged overtly or implicitly with conspiracy theories, strategic constraints prevented Japan’s ruling party, the LDP, from doing so, leaving an open political space for a challenger party like the Sanseito. By studying the Sanseito using the framework of challenger party theories and engaging with a comparative analysis of how parties in other developed nations have reacted to the rising influence of conspiracy theory narratives among their citizenry, this paper clarifies the contexts in which conspiracy theory movements may coalesce as political parties capable of winning representation, and helps to explain why we have not seen this type of conspiracy-focused challenger party emerging more frequently in other nations.