  Political advertising on digital platforms has grown dramatically in recent
years as campaigns embrace new ways of targeting supporters and potential
voters. Previous scholarship shows that digital advertising has both positive
effects on democratic politics through increased voter knowledge and
participation, and negative effects through user manipulation, opinion
echo-chambers, and diminished privacy. However, research on election campaign
strategies has focused primarily on traditional media, such as television.
Here, we examine how political campaign dynamics have evolved in response to
the growth of digital media by analyzing the advertising strategies of US
presidential election campaigns during the 2020 primary cycle. To identify
geographic and temporal trends, we employ regression analyses of campaign
spending across nearly 600,000 advertisements published on Facebook. We show
that campaigns heavily target voters in candidates' home states during the
"invisible primary" stage before shifting to states with early primaries.
