  Money is central in US politics, and most campaign contributions stem from a
tiny, wealthy elite. Like other political acts, campaign donations are known to
be socially contagious. We study how campaign donations diffuse through a
network of more than 50 000 elites and examine how connectivity among previous
donors reinforces contagion. We find that the diffusion of donations is driven
by independent reinforcement contagion: people are more likely to donate when
exposed to donors from different social groups than when they are exposed to
equally many donors from the same group. Counter-intuitively, being exposed to
one side may increase donations to the other side. Although the effect is weak,
simultaneous cross-cutting exposure makes donation somewhat less likely.
Finally, the independence of donors in the beginning of a campaign predicts the
amount of money that is raised throughout a campaign. We theorize that people
infer population-wide estimates from their local observations, with elites
assessing the viability of candidates, possibly opposing candidates in response
to local support. Our findings suggest that theories of complex contagions need
refinement and that political campaigns should target multiple communities.
