In the push for a December impeachment vote, House Democrats appear poised to make history. It will be the shortest investigation producing the thinnest record of wrongdoing for the narrowest impeachment in history. There is, however, a precedent for the Democrats’ expansive interpretations of bribery and impeachment: the trial of Warren Hastings, 230 years ago in Britain. But Hastings’ tale is a cautionary one that nobody should aim to repeat.

House Speaker Nancy Pelosi says she has “corroborated evidence of bribery.” House...