The first part of this study investigates the engaging nature of populist rhetoric on social media, particularly from populist leaders in power. It suggests populists employ divisive and plebiscitary rhetorical elements to manipulate public opinion, advance their agendas, and potentially dismantle democratic institutions. A comparative analysis of 136,141 tweets from 24 Latin American presidents reveals that populist leaders use significantly more divisive and plebiscitary content than their non-populist counterparts, correlating with increased online engagement. The second part examines millions of replies to these presidents' tweets, employing AI techniques such as Generative Pre-trained Transformers for data augmentation and Bidirectional Encoder Representations from Transformers for text classification. The findings indicate that populist presidents generate more divisive interactions, although non-populist leaders can also evoke such interactions during crises like elections, pandemics, and social unrest. Finally, a survey experiment involving Twitter users from Argentina, Brazil, Chile, and Mexico further demonstrates that populist leaders' digital presence elevates incivility, particularly when they are in power. This research contributes to understanding how populist leaders exploit social media to enhance their political strategy and its implications for democratic erosion in emerging democracies.