“When the user challenged the subpoena in court on free speech and statutory grounds (as many others have), DHS withdrew it.”
DHS lost the fight over its own subpoena, so it went shopping for a different one. A grand jury subpoena needs no judge’s approval, and that’s the whole appeal. The target is an anonymous Reddit commenter who criticized an immigration officer. Nobody has been charged with anything. The point is to make the next critic think twice.