Who Toes the Line? Mandate Type, Open-Primary Experience, and Party Defection in the Korean National Assembly*

Previous studies on legislative voting behavior in the Korean National Assembly (KNA) were based on two theories: "The Best of Both Worlds" vs. "Contamination." However, both these theories have paid limited attention to the electorally vulnerable condition of legislators owing to voting behavior in South Korea. In this study, we propose a conditional mandate-divide theory to elucidate party defection voting behavior in KNA. According to our findings, Proportional Representatives (PR) are more likely to defect from party-line voting than Single Member District (SMD) members, although SMDs elected through a party primary are more likely to defect from party-line voting than other SMDs. Additionally, SMDs elected with the primary experience deviate from their party line more in Yeongnam province compared to other regions. Our findings suggest that legislators' voting behavior in the mixed-member system may vary depending on their prospects of re-election, essentially shaped by their incentive structure.