Sean G. Turnbull displays many of the hallmarks of a successful upper-middle-class family man, a former film producer and marketing manager for one of the country’s largest retail corporations who lives in a well-appointed home in this Twin Cities suburb. Former colleagues describe him as smart, affable and family-oriented. But for more than a decade, the 53-year-old has also pursued a less conventional path: anonymously promoting conspiracy theories about dark forces in American politics on websites and social media accounts in a business he runs out of his home.