The populist spiral: How populist rhetoric spreads within party systems

This paper investigates whether populism, independent of its substantive policy correlates, diffuses within party systems as a rhetorical strategy. Building on theories of political contagion, I argue that populism’s simplicity and flexibility make it an attractive tool for parties seeking to mobilize voters, disrupt competitors, and respond to systemic pressures. Using the V-Party dataset, which provides expert-coded estimates of populist rhetoric across a global sample of parties, I construct a leave-one-out (LOO) Index to capture systemic populist signals. Time-series cross-sectional regression models with fixed effects reveal that higher levels of systemic populism significantly increase the likelihood of parties adopting populist rhetoric in subsequent electoral cycles. The effect is most pronounced for anti-elitism and people-centrism, while pluralistic norms and non-violence remain stable. Right-leaning parties exhibit stronger responsiveness, reflecting the natural alignment between populist themes and conservative platforms.