The attorney general of Washington D.C. filed a lawsuit last week that may contain the missing ingredient for proving antitrust versus Amazon. The lawsuit is about prices: For years, Amazon barred U.S. merchants from selling their goods anywhere else for a lower price, according to the lawsuit. Although that practice was changed in 2019, Washington D.C.'s attorney general contends Amazon replaced it with a policy that is effectively the same. (Amazon denies this.)