This dissertation provides evidence that populist rhetoric shapes Congress, parties and individual politicians in rich and contextual ways. I collected a dataset of over 2 million tweets (2012-2020: Chapter 2) and over 150,000 speeches (110th-116th congresses: Chapter 3) from the congressional record, and analyzed these texts using automated dictionary analysis. Populist language on Twitter was associated with greater engagement (favorites, retweets) and with increased candidate fundraising (dollars, number of donors). Analyzing speeches, members that are ideological extremists and engage in dilatory tactics use populist rhetoric more, while the most productive legislators use it less. My final substantive chapter (4) details survey experiments that gauge the impact of populism on voters' perceptions of Congress as an institution and on candidate perceptions. Candidate characteristics do affect voter perceptions of honesty and authenticity, although overall I caution against the overinterpretation of these results due to their inconsistency and small substantive size.