Populist parties and parliamentary collaboration patterns of co-sponsorship

Prior research shows that the voting behaviour of Members of Parliament (MPs) of populist parties on parliamentary proposals are determined by the same factors that determine such votes of MPs of other parties: Ideology and government/opposition status. We argue that this might be different when it comes to parliamentary behaviour that requires active collaboration between MPs. We expect the openly expressed hostility of populists towards other parties to hinder such collaboration. We analyse a dyadic dataset of all pairs of parties and the extent of collaboration between these two parties. We study four parliamentary periods of the Second Chamber of the Dutch Parliament (pooled and separately) between 5 elections (2006, 2010, 2012, 2017 and 2021). The results show general support for the hypothesis that there is less cooperation between populist and non-populist parties. However, the hypothesis was only supported in the first three parliamentary periods, but not in the period between 2017 and 2021. So, MPs of populist parties are gradually behaving less as ‘outsiders’ than how they publicly present themselves.