It's been long said that a prosecutor could get a grand jury to indict a ham sandwich. A grand jury is a way for a prosecutor to violate the Fourth Amendment. See Tim Lynch, "A Grand Façade: How the Grand Jury Was Captured by Government" (here).
One grand juror started asking a prosecutor too many questions. The prosecutor, assistant U.S. Attorney Daniel Zachem, dismissed the grand juror. The grand juror sued, and the D.C. Court of Appeals held that the prosecutor lacked absolute prosecutorial immunity.
Today the United States Supreme Court decline to review the opinion. Mike Scarcella has more details here.