Any political party has a profound interest in maximizing seats, which in turn requires running the optimum number of candidates. However, to do this presumes solving a collective action problem among self-interested party members or leaders, and is deeply conditioned by the electoral system. The case of Japan’s Liberal Democratic Party under the Single Non-Transferable Vote electoral system provides a superb illustration of how party leaders, even in a famously electorally successful party, will be unable to solve these dilemmas because of key facilitating institutions: first, party president selection rules; second, prime ministerial control over allocation of positions; third, a weak party label. Contrary to existing literature, we find ambitious factions consistently nominated too many candidates – deliberately risking the party’s losing seats. We draw attention to the sources of party strength in a novel way, and to how party rules interact with electoral systems to shape both parties and politics.