Effects of electoral margins on party loyalty in the roll call votes: Evidence from the 20th National Assembly in South Korea

Abstract

In modern democratic politics, members of parliament (MPs) engage in legislative activities influenced by political parties and voters. This article examines how electoral margins within constituencies affect MPs’ party loyalty in roll call votes. We analyzed all bills of the 20th Korean National Assembly (2016–2020), providing evidence for the marginal hypothesis from the perspective of an emerging democratic country. We found MPs were more likely to deviate from the party’s position in roll call votes during their term where voting margins were greater. This relationship was heterogeneous according to MPs’ and local districts’ conditions. We found feedback effects, whereby political parties and voters reflected the MPs’ party loyalty in the subsequent election. These results suggest that in Korea, where pork-centric regionalized politics have become solidified, voters tend to perceive MPs as representatives of political parties, and MPs constrained by tight voting margins seek to follow party discipline to ensure reelection.