Countering Foreign Disinformation on Social Media

What we know about Russia's social-media campaign provides lessons for the future.

It is absolutely fair game and legal — in free countries, at least — for anyone to get online and say whatever he wants about American presidential candidates. If you want to say this candidate is a fool and that candidate is a bad guy, you’re perfectly free to do so.

What you cannot do is go online and pose as someone else. And if you’re a foreign intelligence service, we really don’t want you impersonating citizens of...