Discipline, party switching and policy divergence

We develop a comparative theoretical analysis of weak versus strong party discipline. In our model, political parties first select their policy platform and, in the case of strong party discipline, they set disciplinary penalties; second, candidates select their party label and, once elected, they choose whether to toe their party line in their legislative vote. Political parties maximize vote-share and they care about their candidates' loyalty. Candidates are ideological and try to satisfy some psychological needs such as ambition and reputation. We show that: i) A party attracts more candidates to its party label, the higher its expected vote-share and the smaller the parties' political distinctiveness; ii) Legislators deviating from party-line voting arise within the majority party and provided that there is weak discipline; iii) The more legislators care about ideology and the less about their reputation, the more they deviate from party-line voting; iv) Majority parties with weak discipline can opt for more partisan policies to discourage switching behavior in legislative votes, that is, polarization incentivizes loyalty.