As Dan Rather steps down as anchor of the CBS Evening News on Wednesday, the person who deceived him with fake memos on President Bush's National Guard service last fall remains at large, spared from even the threat of a federal or state investigation. Both federal and state felony statutes exist that give law enforcement authorities the ability to pursue the culprit. But neither the U.S. Department of Justice nor prosecutors in Texas have taken up the cause. A spokesman at the Justice Department told HUMAN EVENTS that federal officials