The vast majority of what we know about building prospective electoral constituencies is confined to single-member district systems. However, most legislators are elected in multimember districts. Given that multiple incumbents represent the same voters, how do legislators decide whom they should target as prospective constituents? We build a general model of this decision and test it with travel data for 100 legislators elected in a single, nationwide district. We find that incumbents protect their existing supporters and avoid bailiwicks dominated by others. We conclude by deducing hypotheses about party system effects on incumbents’ decision making and the level of electoral conflict.