This article has been updated to reflect additional information about the author.

In anticipation of Lt. Col. Alexander Vindman’s recent public testimony in the House’s impeachment inquiry, the Fox News host Laura Ingraham and a guest concocted an insulting fantasy on her show: the idea that Colonel Vindman might be a Ukrainian spy.

It may have shocked a lot of Americans that Fox News televangelists and establishment conservatives like John Yoo are spinning the “narrative” of the courageous Colonel Vindman — a man who put his country’s interests ahead of his own — into one that suggests, as an immigrant, he wasn’t loyal to the United States. But it didn’t shock me. For 14 years, I was a Fox News opinion talk-show guest host and contributor, until the network canceled my contract in 2013 because of a conflict between its contributor policy and my investment-research business.

I can explain the art and purpose behind throwing a Purple Heart veteran under the Fox News bus. First, we must talk about narratives. In my time at Fox News, narratives were weapons of mass emotional manipulation, what the Nobel laureate Robert J. Shiller defines in “Narrative Economics” as “contagious stories” — as he put it in a paper of the same name, “a simple story or easily expressed explanation of events that many people want to bring up in conversation or on news or social media because it can be used to stimulate the concerns or emotions of others, and/or because it appears to advance self-interest.” One recent report said that we find information or misinformation “22 times more memorable in narrative form.”

There’s little in this world that has the emotional manipulative power of a good tribalized — us versus them — narrative. It’s a contagion, and thanks to social media, or “participatory propaganda,” highly viral.