Second-level agenda-setting effects of news media and public policy on social media discourse across platforms: immigration during the COVID-19 pandemic in the U.S.

Integrating intermedia, second-level agenda-setting, and cross-platform research, this study examines the role of news media attention and public policy decisions in driving the salience of issue attributes on multiple social media platforms. We collected three immigration-related datasets (i.e., social media posts, news media headlines, and policy documents covering the first year of the COVID-19 pandemic that also marked the last year of the Trump presidency) and applied manual coding, automated text analysis, and time series modeling to analyze the relationships. The results show that news media set the public agenda across Facebook, Twitter, and YouTube at the second level, with conservative media elevating travel-related discussion and liberal media driving border- and court-rulings-related discussion on those platforms. Compared to news media, the second-level agenda-setting effect of policy announcements was small and platform-specific. Among the three platforms, public discourse on YouTube was the most responsive to media and policy agendas. These findings advance second-level agenda-setting research, demonstrate partisan differences in news media's impact, reveal the limited role of public policy, and provide a nuanced portrayal of cross-platform public discourse dynamics.