Populist rhetoric is widely recognized as distinct from that of mainstream politicians. Yet, little is known about how mainstream adapt to populist success. We examine how mainstream adjust their rhetoric, in both topics selection and ton. Using a unique corpus of over 300,000 speeches from the European Parliament, we confirm that populist rhetoric is significantly more emotional than that of mainstream politicians. Topic selection explains only a quarter of this emotional gap, leaving an extra-emotional component unique to populists. Then, leveraging variations in populist exposure across member states, we show that populist emotional rhetoric is contagious, shaping both the tone and topics of mainstream politicians. This shift is largely driven by a substitution effect, where less emotional mainstream politicians are replaced by those adopting a more emotional style.