Devotees of Qanon — a far-right conspiracy theory about President Donald Trump’s secret war against Hillary Clinton, the so-called deep state and a fictitious global child sex cabal — are showing their devotion to the cause by buying merchandise, including T-shirts, hats, and jewelry, on Amazon.com. Shoppers are presented with over 1,000 results when they search Amazon for the term “Qanon,” a baseless and convoluted theory that mirrors 2016’s “pizzagate” conspiracy, which claimed Clinton was running a child sex trafficking ring out of a Washington pizza shop’s basement and led to a shooting at that restaurant by a pizzagate-believer in...