Scholars have long sought to understand the motivations and behaviour of political parties. Yet parties are not unitary actors, and legislators within the same party may have divergent interests. We argue that, in contrast to their co-partisans, politicians who hold ministerial offices can simultaneously maximize policy, office and votes. Evidence of the divergent incentives and interests of individual legislators within the same party is provided using original data from 5 parliamentary democracies. Election returns from 1980 to 2011 show that senior mega-seat holders are largely insulated from the electoral cost of governing compared to their co-partisans. Differentiating between the interests of mega-seat holders and their co-partisans has broad implications: Our argument potentially helps resolve the puzzle as to why political parties enter government despite anticipated electoral liabilities. Moreover, the previously overlooked electoral benefits of mega-seats help to explain their attractiveness to legislators and thus their ability to incentivise party discipline.
