The Richard Nixon Library would like people to stop describing the firing of FBI Director James Comey as "Nixonian" for one very simple reason: Nixon never fired the director of the FBI.
During the infamous "Saturday Night Massacre" on Oct. 20, 1973, Nixon got rid of Archibald Cox, the special prosecutor in charge of the Watergate investigation, which caused the resignations of Attorney General Elliot Richardson and Deputy Attorney General William Ruckelshaus. This was the tipping point for Nixon's demise, with Congress seeing Cox's dismissal as an abuse of presidential power and the American people quickly coming around to the idea of impeachment.
Through it all, though, Nixon did not fire the FBI director. It's not often that Nixon can have any sort of moral high ground, so let the library have its moment.