What do the Amish lobby, gay wedding vans and the ban of the national anthem have in common? For starters, they’re all make-believe — and invented by the same man. Paul Horner, the 38-year-old impresario of a Facebook fake-news empire, has made his living off viral news hoaxes for several years. He has twice convinced the Internet that he’s British graffiti artist Banksy; he also published the very viral, very fake news of a Yelp vs. “South Park” lawsuit last year. But in recent months, Horner has found the fake-news ecosystem growing more crowded, more political and vastly more influential:...