If Russia interfered in election, what could U.S. do?

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. That makes nonintervention a principle of customary international law, albeit a custom sometimes honored more in the breach.

The idea that states should leave one another alone certainly makes sense. On some level the whole theory of national sovereignty — the cornerstone of modern international law — depends on that idea.

The founding fathers' favorite international law theorist, Emmerich de Vattel, put it this way in 1758: "It clearly follows from the liberty and independence of nations that each has the right to govern itself as it thinks proper, and that no one of them has the least right to interfere in the government of another."

At a minimum, nonintervention means not using coercive force in another country. Russia, of course, didn't use force to intervene in the U.S. election, the way it did in Crimea, for example.

But the International Court of Justice has interpreted the principle of nonintervention to extend beyond force. Its most notable discussion of the issue came in the 1986 case of Nicaragua v. U.S. There, in Paragraph 205 of the judgment, the court said it was unlawful for a state to intervene in a way "bearing on matters in which each State is permitted, by the principle of State sovereignty, to decide freely" — and that included "the choice of a political, economic, social and cultural system, and the formulation of foreign policy."

In a 2005 case, the international court said expressly that the principle as described in the Nicaragua case prohibits a state "to intervene, directly or indirectly, with or without armed force, in support of the internal opposition within a State."

Violations of international law are funny things. Because there is no international super-sovereign, the fact of a violation doesn't usually trigger immediate legal consequences.

The U.S. could certainly sue Russia in the International Court of Justice. But it would have to get over the embarrassment of citing the Nicaragua decision, which went against the U.S. and awarded reparations to Nicaragua for the Americans' support of the Contras, in violation of the principle of nonintervention.

To make matters worse, the U.S. never accepted the result in the Nicaragua case. After appearing in court to say that the international court didn't properly have jurisdiction over it, the U.S. took its ball and went home, refusing to appear and argue during the merits stage. Subsequently, the U.S. made sure to veto United Nations Security Council Resolutions that would have required it to comply with the judgment — a total of six times.

But if the U.S. were nevertheless to seek retaliation against Russia, what remedy would be allowed? The court in the Nicaragua case said that violations of the nonintervention principle would justify "proportionate countermeasures." It made it clear, however, that if the original intervention didn't involve force, countermeasures couldn't involve the use of force, which would be disproportionate.

That means the Russian hacking probably can't be construed as an act of war, at least not of the kind that would justify armed retaliation.

That raises the possibility that the lawful response to Russian efforts to disrupt U.S. elections might be to try to disrupt the Russian political process in return. Ordinarily, that would be an unlawful violation of Russian sovereignty. But just as a violent attack justifies the use of force in return, dirty tricks might justify dirty tricks.

I'm not sure that approach would be wise. As a democracy, the U.S. should be interested in assuring the cleanness of elections, especially because open democracies are the most vulnerable to foreign intervention. Nevertheless, the theoretical possibility exists.

Whether or not the U.S. chooses to retaliate against Russia, we'd do well to keep in mind that as a global superpower, we have done more than our fair share of intervening in other countries' affairs. Russian hacking is an outrage, to be sure. But perhaps the best solution would lie in re-evaluating our own democratic values, so that leaks and fake news don't determine elections in the future.