Building Castles Made of Sand? The Impact of Domestic Issue Polarization on EP Party Unity

Does national level issue polarization predict the national party delegations unity in the European Parliament (EP)? Scholars find that disperse issue-level preferences within political parties can have a detrimental impact on a party’s electability. Fractionalization, within governing parties especially, results in mixed messages to voters over both the parties’ issue positions and their viability to hold office or oversee policy-making. However, these effects can have an even further reaching impact beyond the national political sphere. We propose that diverse preferences within political parties on a host of issue areas can springboard from domestic debates to the supranational level and playout cross-nationally in the EP. As we see more diversity of preferences and polarization of salient issue areas at the national level, we predict that these debates will be further amplified within the EP. In effect, voter and elite salience predicts the degree of polarization within party delegations. To test our argument, we use a multilingual, supervised machine learning approach to construct a new dataset on the content of parliamentary speech and scale party issue preferences in nine EU member states and the EP for the period of 2009-2019.The results of this analysis hold implications for theories of parliamentary agenda formation in multilevel settings. Our findings provide theories of national level debate and disagreement with a key mechanism for influencing EP policy-making process.