Can the United States Deter Threats from Uncertain Origins?

The mystery surrounding the so-called Havana Syndrome — an unexplained illness first experienced by U.S. Department of State personnel stationed in Cuba in late 2016 — illustrates the challenge of mustering a response to a national security threat when the threat, the underlying method, and the actor behind the threat are not understood with certainty. This report explores the applicability of existing concepts for deterrence and compellence using brief case studies. In addition to Havana Syndrome, the authors explore the SolarWinds cyberattack, in which hackers linked to Russian intelligence conducted a massive cyberattack against American companies and government agencies, and the Chinese Communist Party's connections to organized crime syndicates around the world.

The core finding is that few of the standard response options are effective against these types of threats. Without certainty about who is conducting the actions, strategies that rely on threats of punishment, normative taboos, or rallying of international condemnation are largely ineffective. Denial-by-defense strategies are thus likely to be the most effective but may be difficult to design effectively if the method underlying the attacks is poorly understood.