She was an intelligence analyst at the CIA. Now she writes about the dangers of ‘fake news.’

As an intelligence analyst at the CIA, Cindy Otis was trained to assess how our country’s foreign adversaries deploy divisive rumors, destructive conspiracy theories and other kinds of disinformation against us.

Several months after the 2016 presidential election — which saw both the concerted Russian campaign to undermine trust in democracy and a surge in domestically created false content — she decided to leave the agency and deploy her skills on a different front. The analytic skills she had acquired, she reasoned, could be used to help the public learn how to responsibly assess what they’re...