Responding to Whom? Political Parties, Interest Groups and Voters

Do political parties respond to interest groups or to voters? While the responsiveness of political parties to voters has received widespread attention in recent years, little is known about how interest groups affect parties’ policy agendas. In this paper, I argue that political parties respond to interest group mobilization as lobbyists offer valuable information, campaign contributions and personal rewards. However, since political parties need to satisfy voter demands to secure their reelection, interest groups are particularly able to shape the policy agenda of political parties when they prioritize policy issues that are also important to voters. The theoretical expectations are tested based on a novel empirical analysis that combines an innovative and unprecedented longitudinal dataset on interest group mobilization with data on parties' issue emphasis in election manifestos obtained from the Manifestos Project and data on voters' issue priorities gathered from public opinion surveys. Based on a longitudinal analysis studying the responsiveness of German parties across eleven issue areas and eight elections from 1987 until 2013, it is shown that parties adjust their policy agendas in response to interest group mobilization and voter demands and that interest groups are more successful in shaping party policy when their priorities coincide with those of the electorate.