Correct answer:
He fired the attorney general for refusing to fire the special prosecutor.
Saturday Night Massacre was the name given to a series of events that took place in the United States on October 20, 1973.
During the scandal, President Nixon's first reaction was to dismiss the attorney general for refusing to fire the special prosecutor; in the second instance, he appealed to Deputy Attorney General William Ruckelshaus to dismiss the special prosecutor, but he also refused. He had to take the order to a third instance, where the Attorney General took that order to term.