Donald J. Trump was chastised on Tuesday by the judge presiding over his civil fraud trial after the former president posted a message targeting the judge’s law clerk. Mr. Trump attacked the clerk, Allison Greenfield, shortly before noon on his Truth Social site. His post was a picture of Ms. Greenfield with Senator Chuck Schumer, the Democratic majority leader. Mr. Trump mocked Ms. Greenfield as “Schumer’s girlfriend” and said that the case against him should be dismissed.