This study creates a theoretical connection between ideological congruence and political polarization. In recent years there is a growing body of literature that deals with political
polarization, seeing it mainly as a top-down phenomenon. However, this research claims that political polarization is rather a bottom-up phenomenon, that generates in the ideological
differences between the different segments within political parties.
Political parties are usually composed of four layers: elites, activists, members, and voters. Compared to other groups, party activists are well known for their extreme preferences and their uncompromising ideological character. This characteristic, when combined with political power, can enable party activists a significant influence over party elite preferences. The procedure of candidate selection can serve as the political opportunity for party activists to gain influence inside the party, and thus tip the party's ideological balance towards their preferences. If party activists can assert their control over this process, they will be able to move elite preferences away from the more moderate opinions of the party's voters and closer to their own extreme positions. This study argues that an increase in party activists intra-party political power causes a decrease in ideological congruences between party's elite and voters, and increases the level of political polarization in the party system.
In this paper, I utilize data from both CSES model 4 and the newly published Political Party Database. I examine my theory in a comparative perspective in 19 western democracies. In a preliminary analysis I find support for my research hypothesizes.
