The growing salience of Euroscepticism among both voters and parties has shifted the structure of political conflict in the European Parliament (EP) from traditional left-right competition towards an increasingly dominant pro-/anti-EU cleavage. Focusing on EU enlargement as a test case, we explore the emergence of this cleavage at different levels of MEPs’ legislative behaviour over the past two EP mandates (2009-2019). Drawing on two original datasets containing 1’250 MEP statements on enlargement in EP debates with their vote choice across 47 subsequent roll-call votes, we show a growing polarisation around enlargement issues: although discursive support for enlargement declines for all party groups, we observe a sorting of MEPs into two distinct camps that represent opposing views. Polarisation is even starker for roll-call votes. Finally, we find increasing coherence between discursive and voting behaviour for Eurosceptics that contrasts with an emerging discourse-vote choice gap for pro-European party groups. Our findings show that polarisation is primarily driven by soft Eurosceptics who become firmer in their rejection of further enlargement, ultimately leading to a consolidation of the pro-/anti-EU cleavage as main divide in the EP.
