How Should Sanctions Account for Bystander Countries?

Neutral “bystander countries” have profoundly shaped the impact of trade sanctions imposed on Russia following its invasion of Ukraine. How should sanctions account for the presence of such bystanders? I study this question in a simple trade model where a sanctioning country places tariffs on imports from a sanctioned country in the presence of a neutral third country. Optimal tariffs-as-sanctions are lower on goods that the sanctioner can import from bystanders. On goods that the sanctionee can export to bystanders, tariffs-as-sanctions are higher given an elasticity of (excess) supply to the sanctioner but lower given a total elasticity of supply.