By taping conversations in the Oval Office, President Richard Nixon was not violating the rights of the people he taped. In fact, Franklin D. Roosevelt and JFK already used a tapping system. The District of Columbia law allows taping conversations as long as at least one participant is aware that there is a recording being made.
A different issue is if those recordings might be evidence of criminal activity. Richard Nixon tried to gain control over the tapes after the federal government seized them, stating that it infringed his personal privacy rights, but he died before the resolution of the legal battle.