In a world of big data, with more information at the audience’s fingertips than ever, gatekeepers such as media and political parties still play a huge role in mediating issues to the general public. Recognizing this issue, this study investigated the first and second levels of intermedia agenda setting between political advertisements, newspapers, and Twitter postings (tweets) about Barack Obama and Mitt Romney during the 2012 U.S. presidential election. A series of computerized content analyses with ARIMA time-series modeling were employed. Our findings will extend agenda-setting theory to the social media environment.