  Social media provides a critical communication platform for political
figures, but also makes them easy targets for harassment. In this paper, we
characterize users who adversarially interact with political figures on Twitter
using mixed-method techniques. The analysis is based on a dataset of
400~thousand users' 1.2~million replies to 756 candidates for the U.S. House of
Representatives in the two months leading up to the 2018 midterm elections. We
show that among moderately active users, adversarial activity is associated
with decreased centrality in the social graph and increased attention to
candidates from the opposing party. When compared to users who are similarly
active, highly adversarial users tend to engage in fewer supportive
interactions with their own party's candidates and express negativity in their
user profiles. Our results can inform the design of platform moderation
mechanisms to support political figures countering online harassment.
