<p>In this paper, we analyse the evolving role of hate speech in political rhetoric in Spain over the past three decades, focusing on its impact on electoral outcomes. Through a longitudinal analysis of political discourse in Parliament using Natural Language Processing (NLP), we calculate the likelihood of hate speech and we find significant changes in the frequency and intensity of inflammatory speeches made by politicians. Our findings suggest that hate speech is linked to higher voter mobilisation, indicating that such rhetoric may influence voter turnout and election dynamics. Furthermore, we show that since the rise of the extreme-right party in Parliament in 2019, that tendency has shifted, and parties that refrained from using hate speech tended to attract more voters, highlighting the potential electoral cost of employing divisive language. Additionally, we show how this party influenced others to escalate their rhetoric, increasing in some cases the likelihood of hate speech by around 200% in less than 5 years. This study contributes to understanding the use of hate speech by politicians in Parliament in polarising political discourse and marginalising minority groups.</p>