Party Ideology, Institutions, and Elite Hostile Rhetoric: When Does Online Communication Turn Antagonistic?

Elite hostile rhetoric is a defining feature of online communication on social platforms. Yet, not all hostility is equally detrimental to democratic life. Drawing on agonistic democratic theory, this paper distinguishes agonistic hostility (rhetoric that treats opponents as legitimate rivals) from antagonistic hostility (which portrays them as illegitimate enemies). We ask a simple but underexplored question: given that social media rewards conflictual content across the board, why do the types of hostility that elected officials adopt vary across parties and democracies? To answer that question, we argue that both the intensity and the kind of hostility in elite political communication are driven by two nested incentive structures, namely institutional regimes and party-system configurations. At the party level, radical and populist challengers have incentives – emotional styles and strategic positioning in the party system – to escalate conflictual rhetoric compared to mainstream parties. At the regime level, majoritarian systems’ winner-take-all logic rewards zero-sum antagonistic rhetoric, while proportional regimes, where coalition cabinets require inter-party cooperation, moderate it. Testing these two mechanisms jointly has been obstructed by fragmented scholarly traditions using different definitions of hostile rhetoric, and by empirical work that relied predominantly on case study or indirect measurement (expert survey), instead of direct measurement of rhetoric across partisan and institutional contexts. We address this gap using the framework of the Political Hostility Scale (PHoS; Dodeigne, 2025; Vargiu, Dodeigne, Nai, 2026) and a supervised deep-learning classifier applied to 2.1 million tweets by elected politicians across 27 democracies (2017–2019). Our results show that hostility follows a U-shaped pattern across the left-right ideological spectrum, with parties at both extremes more hostile than mainstream centrist party families. Yet, this symmetry breaks down for the most democratically damaging rhetoric: antagonistic hostility that frames opponents and social groups as threats is disproportionately concentrated on the radical right. Institutional context matters throughout, with majoritarian systems amplifying these dynamics relative to proportional regime types. Together, these findings offer a theory-driven, empirically grounded account of how institutional design and party competition jointly shape the rhetorical boundaries of democratic contestation – and why the same incentive structures produce democratically compatible hostility in some contexts, but corrosive rhetoric in others.