According to Borrell Associates, digital advertising made up a small fraction
(less than 1 percent, $71 million) of political ad spending in the United States in
2014 but was projected to comprise a ﬁfth of spending (20.1 percent,
$1.8 billion) in 2018 (Borrell Associates 2018). Although digital advertising in
campaigns has been around for a while and has been a growth market for
several cycles now, it has long been overlooked by scholars, especially in
comparison to traditional television advertising, for which there is a long and
robust literature (see Fowler, Franz, and Ridout 2016), and even organic social
media content, for which there is burgeoning research (Borah 2016; Bode et al.
2016). The lack of research on paid online advertising stems, in large part, from
the difﬁculty in tracking the placement of and spending on online ads on
websites, in apps, and on social media. Unlike television, where commercial
tracking data has been available for two decades, systematic commercial
Social_Media_and_Democracy