I think the analogies between Sally Q. Yates dismissal by Trump and Nixon's dismissal of Archibald Cox are misplaced. Trump was well within the legal parameters of his job description to fire Yates. Nixon was under investigation by Cox at the direction of Attorney General Richardson who hired Cox as special prosecutor after being directed to do so by Congress. The only way that Cox could be fired was if he failed to do his job. Nixon fired Cox because he was doing his job. Afterwards a federal judge determined that Nixon was in error, and he required Nixon to appoint a new special prosecutor, Judge Sirica (that's the right name I believe.) Nixon tried to appoint someone who he thought would not pursue the investigation heartily, but Sirica did indeed pursue the investigation and the rest is history.

Also Richardson was not fired, he resigned after determining that he could not sign off on Nixon's dismissal of Cox. Then Richardson's deputy resigned because he too felt the same way. Then the person who was next in line, the solicitor general, agreed to sign off on the dismissal, so Nixon had him sworn in as acting AG and Cox was fired. The solicitor general was Robert Bork, and his firing of Cox meant that later when Bork was nominated to the Supreme Court by Reagan, there was no way in hell the Democrats were going to let him reach the bench.