The recent appointment of Stephen K. Bannon, the right-wing media mogul, as chief executive of Donald J. Trump’s campaign was part of an effort to reset a candidacy that has stumbled with minority and female voters and suffered from controversies surrounding high-level campaign officials.

But Mr. Bannon brings to the post his own bumpy background that includes misdemeanor charges of domestic violence and allegations that he threatened his then wife, the accuser, with retribution if she testified in the criminal case, according to a police report of the incident and court records obtained by The New York Times.

The charges date back two decades to the end of a troubled marriage in Santa Monica, Calif., when Mr. Bannon’s wife, Mary Louise Piccard, claimed that he had attacked her at their home.

He was charged in February 1996 with domestic violence, battery and attempting to dissuade a victim from reporting a crime, but the case was dropped when Ms. Piccard did not show up in court. In court records, Ms. Piccard later claimed that Mr. Bannon instructed her to leave town to avoid testifying.