Complexity of Control by Partitioning Veto and Maximin Elections

Control by partition refers to situations where an election chair seeks to influence the outcome of an election by partitioning either the candidates or the voters into two groups, thus creating two first-round subelections that determine who will take part in a final round. In particular, “gerrymandering” (maliciously resizing election districts) can be modeled by partition-of-voters control attacks. While the complexity of control by partition (and other control actions) has been studied thoroughly for many voting systems, such results about the important systems veto and maximin voting are sparse. We settle the complexity of control by partition for veto in a broad variety of models and for maximin with respect to destructive control by partition of candidates.