This dissertation is about patterns of alliance and opposition evident in records of financial contributions to federal political campaigns. Over periods of many years, repeat donors develop affiliations with specific candidates and organizations. Similarly, candidates, organizations, and incumbent lawmakers cultivate overlapping sets of contributors. Scholars have used these intersecting financial ties to infer estimates of donor and candidate ideology on a liberal-to-conservative continuum. While this has helped to break new ground in the study of partisan polarization, these methods have offered little purchase on questions of within-party structure. As the need to understand polarization becomes more acute, and ongoing research more strongly signals that it is an intrapartisan as well as interpartisan phenomenon, this has become an increasingly important problem to solve. This dissertation introduces a way forward through an extension of existing methodological work. This project makes three key contributions. First, it presents a new procedure for inference about communities of donors and candidates in federal campaign finance. This section of the dissertation demonstrates the gains to be made by relaxing the assumptions of existing rational choice approaches and instead adopting a more general network-based interpretation of the ties implied by campaign finance transactions. Next, the work turns to an analysis of the dynamics of conflict between fractions within parties. Here, analysis leads to the conclusion that cohesive action by economic radicals in the Republican Party produces the election of lawmakers deeply embedded in a unique financial community with no real analog on the left. Finally, the dissertation shows that these financial ties also predict substantial and significant differences in the legislative effectiveness of economically radical legislators once in office. Taken together, these findings challenge existing conceptions of the role of campaign donors in federal politics, and promote new directions for political research.