Partners at Arm’s Length: Support Parties and Differentiation Strategies

This paper analyses how support parties use parliamentary behaviour to differentiate themselves from government. I draw on two datasets covering Spanish parliamentary politics. A dataset of more than 96,000 amendments introduced in the Spanish Congress between 1996 and 2023, and a dataset covering more than 11,000 parliamentary votes from December 2011 to June 2026. The analysis focuses particularly on support parties, comparing them to junior coalition partners and opposition parties, and examines whether their use of amendments and vote defections changes when electoral incentives increase, using regional and European elections as windows of higher electoral pressure. The results are mixed. While some parties appear to use these parliamentary tools to differentiate themselves from government, others show little or no change. Overall, the findings suggest that differentiation strategies are not uniform and invites further research into how parties navigate the tensions between cooperation and electoral competition in collaborative environments.