Nixon always denied being directly involved in setting up the dirty tricks. In 1973-74, congressional and federal investigators tried and failed to find evidence to the contrary.
Chapin made his news-making accusation in an interview with Tim Naftali, director of the Nixon library. Go here and listen to Chapin talk about being buzzed into Nixon's office to get the fateful order, deciding to hire his USC classmate Donald Segretti to run the unit, and lining up Nixon's personal attorney, Herb Kalmbach, to pay for it.
The three went to jail as a result of the Watergate scandal. In judging Chapin's late hit, remember that he was convicted in federal court of lying under oath.
The interview appears among the background materials for the Nixon library's upcoming Watergate exhibit, which was attacked by Chapin's White House friends last summer. It will be interesting to see if the interview will be aired by C-SPAN along with Naftali's other revealing chats with Nixon's men.

