Do Islamic State's Deadly Attacks Disengage, Deter, or Mobilize Supporters?

What are the consequences of committing violent attacks for terrorist organizations? Terrorist attacks might broaden the base of supporters by increasing the perceived group efficacy. However, terrorist attacks might also lead its supporters to believe that the organization is excessively violent or involvement may become too dangerous. This article employs a unique dataset with 300,842 observations of 13,321 Twitter accounts linked to the Islamic State (IS), collected during a 127-day period, to empirically investigate the impact of terrorist attacks on the number of the organization's supporters. By exploiting the exogenous timing of terrorist attacks as a natural experiment, we find that the number of followers of IS-related Twitter accounts significantly reduces in the aftermath of the attacks. Additionally, we provide some suggestive evidence to disentangle two mechanisms: disengagement - a change in supporters' beliefs - and deterrence - demobilization due to fear. Because we do not find support for the latter, we conclude that the disengagement effect might explain our main result.