This article offers a theory of how party networks divide the labor of attacking opponents. Using an extensive data set of campaign advertising from the 2010 and 2012 congressional elections augmented with Nielsen television ratings data, it is shown that candidates attack opponents less when supporting outside groups attack more. Due to differences in how outside groups and candidates attack opponents, when candidates partially outsource attack advertising to independent expenditure groups, attacks in that campaign become more issue and policy based. Thus, in perhaps an unintended consequence of the divided labor of attack advertising, outside group involvement makes it more likely that an election campaign will foster citizen knowledge about policy positions of the candidates.