How do the dynamics of portfolio allocation work within parties? While much of the existing literature focuses on portfolio allocation among parties in coalition governments, bargaining over cabinet portfolios also takes place within parties because many parties have internal divisions or factions that influence these decisions. By analyzing data on portfolio allocation in the Liberal Democratic Party of Japan from 1960 through 2007, this study demonstrates that, contrary to the proportionality proposition (Gamson's Law), substantial variance exists in allocation outcomes over time because party leaders allocate cabinet portfolios among factions as a means of preventing defections and challenges from their party's members. The resulting portfolio allocation reflects the bargaining dynamics within the party: I find that party leaders surrender more portfolios as they become more vulnerable to challenges posed by internal rivals.