Presidential campaigns in recent years have shifted their strategy to focus increasingly on base partisans, a shift that has had significant consequences for democracy in America.Over the past few decades, political campaign strategy in US elections has experienced a fundamental shift. Campaigns conducted by both Republicans and Democrats have gradually refocused their attention increasingly toward their respective partisan bases. In Bases Loaded, Costas Panagopoulos documents this shift toward base mobilization and away from voter persuasion in presidential elections between 1956 and 2016. His analyses show that this phenomenon is linked to several developments, including advances in campaign technology and voter targeting capabilities as well as insights from behavioral social science focusing on voter mobilization. Demonstrating the broader implications of the shift toward base mobilization, he links the phenomenon to growing turnout rates among strong partisans and rising partisan polarization. A novel, data-rich account of how presidential campaigns have evolved in the past quarter century, Bases Loaded argues that what campaigns do matters—not only for election outcomes, but also for political processes in the US and for American democracy.