Popular party preferences and legislative party switching

In many contemporary democracies it is common for the members of parliament (MPs) to leave their parliamentary parties to defect to other parties, to create new parties, or to become parliamentary independents. Although the decline in party’s popular support has been proposed as an important factor of legislative party switching, this explanation remains theoretically under-developed because this relationship is likely to depend on the type of switching, electoral vulnerability of individual MPs, and election proximity. Our study addresses this challenge by arguing that legislators in the parties that lose popular support are more likely to defect to other – already existing or new - parliamentary parties than to become independents. Moreover, decline in party support should make defections more likely when MPs are electorally vulnerable and next national parliamentary election is proximate in time. Empirically, our contribution is to test these arguments using a new dataset that covers three Central and Eastern European countries (Lithuania, Poland, and Romania) in the period between 2000 and 2020. We record nearly 1,000 cases of individual decisions to defect to existing parliamentary parties, create new parties, or become independents, and use information from approximately 2,500 individual polls on party support. Our findings have important implications for understanding the representational implications of party switching and complement existing work that demonstrates the impact of public’s party preferences on parliamentary voting unity.