FILE - In this April 17, 1973 file photo, President Richard Nixon speaks during White House news briefing in Washington. President Donald Trump‚Äôs surprise firing of FBI Director James Comey drew swift comparisons to the Nixon-era "Saturday night massacre.‚Äù Both cases involve a president getting rid of an official leading an investigation that could ensnare the White House, said Douglas Brinkley, a presidential historian at Rice University. (AP Photo/Henry Burroughs. File)