Party Coalitions and Interest Group Networks

We analyze affiliation networks of interest groups that endorse the same candidates in primary elections, donate to the same candidates in general elections, and voice support for the same legislative proposals. Patterns of interest group ties resemble two competing party coalitions in elections but not in legislative debate. Campaign endorsement and financial contribution ties among interest groups are consistently correlated but legislative ties do not follow directly from electoral alliances. The results challenge the consensus in the emerging literature on the expanded party organization; interest groups have distinct incentives to join together in a party coalition in elections but also to build bipartisan grand coalitions to pursue legislative goals. We also modify conventional views on party differences. The Democratic coalition is not fractured into many small constituencies. The Democratic campaign and legislative networks are denser than equivalent Republican networks, with a core of labor organizations occupying central positions.