  We study the emergence of support for Donald Trump in Reddit's political
discussion. With almost 800k subscribers, "r/The_Donald" is one of the largest
communities on Reddit, and one of the main hubs for Trump supporters. It was
created in 2015, shortly after Donald Trump began his presidential campaign. By
using only data from 2012, we predict the likelihood of being a supporter of
Donald Trump in 2016, the year of the last US presidential elections. To
characterize the behavior of Trump supporters, we draw from three different
sociological hypotheses: homophily, social influence, and social feedback. We
operationalize each hypothesis as a set of features for each user, and train
classifiers to predict their participation in r/The_Donald.
  We find that homophily-based and social feedback-based features are the most
predictive signals. Conversely, we do not observe a strong impact of social
influence mechanisms. We also perform an introspection of the best-performing
model to build a "persona" of the typical supporter of Donald Trump on Reddit.
We find evidence that the most prominent traits include a predominance of
masculine interests, a conservative and libertarian political leaning, and
links with politically incorrect and conspiratorial content.
