Parties’ Ideological Cores and Peripheries: Examining How Parties Balance Adaptation and Continuity in Their Manifestos

How do political parties balance policy adaptation with ideological continuity? While spatial models emphasise external factors driving party behaviour, less attention has been given to internal party choices. This article innovates by proposing that parties differentiate between and make distinct strategical decisions regarding their ideological core and peripheral policy areas. We argue that parties maintain continuity in their ideological core while exhibiting greater flexibility in modifying their periphery. Using the Manifesto Project Corpus and an XLM-RoBERTa-based language model, we analyse manifesto sections to distinguish core from peripheral segments. Our findings show that parties take clearer stances in their ideological core while adapting their periphery more flexibly, with niche parties displaying this pattern more strongly than mainstream parties. Electoral setbacks lead parties to adopt more extreme peripheries, while cores remain stable. These results highlight the strategic importance of the core–periphery distinction in party communication and suggest that studies of party competition should consider where policy shifts occur within parties’ electoral programmes.