How Conspiracy Theories Are Shaping the 2020 Election—and Shaking the Foundation of American Democracy

Kelly Ferro is a busy mom on her way to the post office: leather mini-backpack, brunet topknot, turquoise pedicure with a matching ombré manicure. A hairdresser from Kenosha, Wis., Ferro didn’t vote in 2016 but has since become a strong supporter of Donald Trump. “Why does the news hate the President so much?” she says. “I went down the rabbit hole. I started doing a lot of research.”

When I ask what she means by research, something shifts. Her voice has the same honey tone as before, and her face...