  Nowadays, social media represent persuasive tools that have been
progressively weaponized to affect people's beliefs, spread manipulative
narratives, and sow conflicts along divergent factions. Software-controlled
accounts (i.e., bots) are one of the main actors associated with manipulation
campaigns, especially in the political context. Uncovering the strategies
behind bots' activities is of paramount importance to detect and curb such
campaigns. In this paper, we present a long term (one year) analysis of bots
activity on Twitter in the run-up to the 2018 U.S. Midterm Elections. We
identify different classes of accounts based on their nature (bot vs. human)
and engagement within the online discussion and we observe that hyperactive
bots played a pivotal role in the dissemination of conspiratorial narratives,
while dominating the political debate since the year before the election. Our
analysis, on the horizon of the upcoming U.S. 2020 Presidential Election,
reveals both alarming findings of humans' susceptibility to bots and actionable
insights that can contribute to curbing coordinated campaigns.
