On the buyability of voting bodies

We study vote buying by competing interest groups in a variety of electoral and contractual settings. While increasing the size of a voting body reduces its buyability in the absence of competition, we show that larger voting bodies may be more buyable than smaller voting bodies when interest groups compete. In contrast, imposing the secret ballot is an effective way to fight vote buying in the presence of competition, but much less so in its absence. Regardless of competition, the option to contract on both votes and outcomes is worthless, as it does not affect buyability compared to contracting only on votes. The option to contract on votes and vote shares, on the other hand, is extremely valuable: it allows the first mover to effectively nullify competition and obtain its preferred policy at almost the monopoly cost.