Paul Callan is a CNN legal analyst, a former New York City homicide prosecutor and currently is of counsel at the New York law firm of Edelman & Edelman PC, focusing on wrongful conviction and civil rights cases. The opinions in this article belong to the author.

(CNN) It was a wet and dreary Saturday on October 20, 1973, when the last Attorney General of the United States was forced to resign rather than follow an order of his boss -- the President of the United States.

On that day, Elliot Richardson defied an order of President Richard Nixon to fire a tough, bow-tied prosecutor named Archibald Cox, a special prosecutor appointed to investigate the Watergate scandal.

Mr. Cox was getting a little too close for presidential comfort to issuing a subpoena for secretly taped conversations between Mr. Nixon and his top co-conspirator aides, H.R. "Bob" Haldeman and John Ehrlichman.

What followed became known as the Saturday Night Massacre . After Mr. Richardson resigned, his deputy attorney general also refused to follow the order -- and was fired by Nixon.

The next in the chain of command was Robert Bork, the Solicitor General of the United States. Bork willingly followed Nixon's order terminating Archibald Cox in an act that would only temporarily stall Nixon's slow march to disgrace and resignation. Bork would subsequently be denied a seat on the Supreme Court.

A chill wind blew through DC again last night, when history repeated itself in a considerably less dramatic "Monday night massacre." President Donald Trump suddenly fired acting Attorney General Sally Yates. Ms. Yates had ordered attorneys at the Department of Justice to refrain from defending the President's executive order mandating strict travel restrictions on the residents of seven Muslim-majority nations in pending court challenges throughout the United States.

The attorney general is, after all, the president's lawyer, whose sworn duty is to defend the president and government of the United States. Ms. Yates suggests that she owes a superior duty to defend the Constitution of the United States and that the sacred principles of that document are being trashed by Mr. Trump.

It should be noted that Ms. Yates was appointed to her position as acting Attorney General by President Obama following the resignation of her controversial predecessor, Loretta Lynch.

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Yates had really just been warming the very hot attorney general seat until Trump's nominee, the equally controversial Sen. Jeff Sessions, is approved by the Senate. She would then have presumably been swiftly replaced, but her retirement has been hastened by a newly elected President, bound and determined to deliver on his every campaign promise in his first two weeks in office.

Yet another controversial promise will surface this evening, when the President announces the name of his first Supreme Court nominee . Ironically, this nominee may -- in his or her vote on the Supreme Court -- help to determine whether Ms. Yates is viewed as a hero or a hack in her refusal to defend the President; the legality of the Trump order may well wind up in the Supreme Court.

Ms. Yates will be forcefully criticized for her obstinacy in refusing to defend the President, particularly if reports that the DOJ Office of Legal Counsel signed off on the form and legality of the controversial executive order before it was issued are true.

The approval of the order does not appear on the OLC website, but more will undoubtedly be heard on this in the days to come.

Ms. Yates' supporters included a suddenly dry-eyed Sen. Chuck Schumer, who suggested that she is a public servant of impeccable integrity. And at least four federal courts seem to agree with acting Attorney General Yates that the executive order in question may have constitutional problems.

On the other hand, a lawyer doesn't have to endorse a client's position to defend it in court. Even guilty criminal defendants have the right to competent counsel. Counsel's professional responsibility is to present the client's strongest case within the bounds of ethics and law.

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Even though the media wind seems to be blowing against Mr. Trump, the legality of the order may be a closer call. The courts have traditionally deferred to the chief executive on matters of foreign policy and security issues relating to the borders of the US. That is not to say that Trump's position is correct but only that it is close enough to the legal line that an ethical lawyer at the Department of Justice could probably offer a defense of the President in good faith.

Elliot Richardson stepped into American history as a man whose honor and courage gave him the strength to protect the nation from an egotistical president who had criminally abused his power and disgraced his office. Ms. Yates may be viewed as a political partisan looking for a flashy exit, or she may share a bit of Elliot Richardson's spotlight. In the end though, I suspect the "Monday night massacre" will never be in the same league with the one that happened on that Saturday so long ago.