How U.S. Could Retaliate for Russian Intervention

If Russia really tried to throw the U.S. election to Donald Trump, what then? Did the hacking violate international law? And if so, what can the U.S. do to retaliate? The short answer is that trying to change the outcome of another country’s election does violate a well-recognized principle of international law, and the U.S. would be legally justified in taking “proportionate countermeasures.” But, in a painful twist, the best precedent comes from a 1986 case the U.S. lost and never accepted.

There are essentially two ways to establish a principle of international law: by treaty or by custom -- and there’s no explicit treaty prohibiting nations from intervening in one another’s affairs.1481566510790 That makes nonintervention a principle of customary international law -- albeit a custom sometimes honored more in the breach.