Since the F.B.I. raid on former President Donald Trump’s home, Mar-A-Lago, the phrases “civil war” and “lock and load” have trended on right-wing social media. The F.B.I. and the Department of Homeland Security are taking the threats seriously, and issued an internal warning that detailed specific calls for assassinating the judge and the agents involved in authorizing and carrying out the search. Where could this all be headed? David Remnick talks with Barbara F. Walter, the author of the new book “How Civil Wars Start: And How to Stop Them.” Walter is a political scientist and a professor at the University of California, San Diego, and a co-director of the online magazine Political Violence at a Glance. She has studied countries that slide into civil war for the C.I.A., and she says that the United States meets many of the criteria her group identified. In particular, anti-democratic trends such as increased voting restrictions point to a nation on the brink. “Full democracies rarely have civil wars. Full autocracies rarely have civil wars,” she says. “It’s the ones that are in between that are particularly at risk.”

This segment was originally aired January 7, 2022.