Republican Sen. Lindsey Graham, the chief apologist for President Donald Trump, walked out of the Senate chambers last week before his remarks about impeachment from 1999 were broadcast.

He had to.

At that moment, Graham became one of chief prosecution witnesses against Trump.

I’ve written about this before. Graham, who was arguing at the time for impeachment of then-President Bill Clinton, said in part:

"You don’t even have to be convicted of a crime to lose your job in this constitutional republic. If this body determines that your conduct as a public official is clearly out of bounds in your role. Because impeachment is not about punishment. Impeachment is about cleansing the office. Impeachment is about restoring honor and integrity to the office."

Yes, that’s exactly it.

Hamilton and Dershowitz agree

Or, as Alexander Hamilton wrote about impeachment in the Federalist Papers, “The subjects of its jurisdiction are those offenses which proceed from the misconduct of public men, or, in other words, from the abuse or violation of some public trust.”

Trump has no defense to such a charge. The evidence and the testimony shows the degree to which he abused his power and, therefore, the public trust.

The president's attorney, former law professor Alan Dershowitz, said recently, “Abuse of power, even if proved, is not an impeachable offense."

Clearly it is, however, which Dershowitz, like Graham, admitted years ago during the Clinton trial, saying, “It certainly doesn’t have to be a crime if you have somebody who completely corrupts the office of president and who abuses trust and who poses great danger to our liberty. You don’t need a technical crime.”

The only remaining question has to do with U.S. senators honoring their oaths.

For that, I would defer to something the late Sen. John McCain — once considered the mentor of Graham — said at the end of Bill Clinton’s impeachment trial.

Then there's the McCain rule

McCain said:

“All of my life, I have been instructed never to swear an oath to my country in vain. In my former profession, those who violated their sworn oath were punished severely and considered outcasts from our society.

“I do not hold the President to the same standard that I hold military officers to. I hold him to a higher standard. Although I may admit to failures in my private life, I have at all times, and to the best of my ability, kept faith with every oath I have ever sworn to this country. I have known some men who kept that faith at the cost of their lives.

“Presidents are not ordinary citizens. They are extraordinary, in that they are vested with so much more authority and power than the rest of us. We have a right; indeed, we have an obligation, to hold them strictly accountable to the rule of law.”

EJ Montini is a columnist at the Arizona Republic, where this column originally appeared. Follow him on Twitter: @ejmontini.