Donald Trump has violated his oath. Mitch McConnell is about to violate 2 of them. Every senator has a constitutional obligation of impartiality. But Mitch McConnell’s role as Senate leader makes his obligation even more important.

Kent Greenfield | Opinion contributor

Show Caption Hide Caption McConnell blasts House over Trump impeachment Senator Mitch McConnell, the top Senate Republican, denounces the "unfair" House impeachment of President Donald Trump and reassured Trump and his supporters that "moments like this are why the United States Senate exists.” (Dec. 19)

We Kentuckians know that our word is our bond. Oaths are the most solemn of promises, and their breach results in serious reputational — and sometimes legal — consequences.

President Donald Trump will soon be on trial in the Senate on grounds that he breached one oath. Senate Leader Mitch McConnell is about to breach two.

The Constitution mentions an oath only three times in its main body. The most famous is the oath the president swears upon taking office, set out word for word in Article II. That article is otherwise quite vague and abstract in describing the president’s powers and obligations. Constitutional scholars have debated for 200 years what the “executive power” means, for example.

But the framers of the Constitution thought the specific words of the oath mattered, and every president has sworn to “faithfully execute the Office of the President … and … preserve, protect and defend the Constitution.” (When Chief Justice John Roberts flubbed the words in President Barack Obama’s first inauguration in 2008, they performed a do-over the next day.)

The core of this presidential oath is faithfulness. This promise mirrors the responsibility mentioned later in Article II that the president “shall take care that the Laws be faithfully executed.” These are the only two times in the Constitution that faithfulness is mentioned. It is the central presidential obligation. The opposite of faithfulness? Corruption and abuse of power. And those constitutional sins, of course, are exactly the basis of the House's vote to impeach President Trump and will be the focus of the Senate’s trial.

Trump isn't the only oath taker

A second oath in the Constitution is in Article VI, which requires all state and federal officers to swear an “Oath … to support this Constitution.” This was a big deal to the framers. The Constitution was the “supreme law of the Land” and even state officials were henceforth “bound by Oath” to it. Like all U.S. senators, congressional representatives, state governors and judges, and other officials, Sen. Mitch McConnell took this oath when he took office.

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The third oath is the rarest. In Article I, the Constitution gives the Senate the “sole” power to “try all impeachments,” and the Constitution requires that “when sitting for that Purpose, they shall be on Oath or Affirmation.” This special oath only kicks in when the Senate tries an impeachment, and this will be only the third time when a president has been so tried. The framers wanted to make sure the Senate would never take such a trial lightly — this oath requirement is over and above the oath each senator has already taken to support the Constitution.

The Constitution does not set out the text of the trial oath, but the Senate rules do. Senators will ‘‘solemnly swear ... that in all things appertaining to the trial of the impeachment of Donald J. Trump, now pending, I will do impartial justice according to the Constitution and laws: So help me God.’’

The presidential oath and the senatorial oath to be taken before an impeachment trial are kin. The president must act faithfully and without corruption. In those (presumably) rare situations in which the president has failed to be faithful, the Senate is required to be faithful in its adjudication of the case against him.

McConnell's rotten trial

But we have already seen indications that McConnell has no intention of doing impartial justice. He has said that he does not consider himself an “impartial juror.” He is coordinating strategy with the White House. He has already called the case against the president “thin” and “incoherent.”

Every senator has a constitutional obligation of impartiality. But McConnell’s role as Senate leader makes his obligation even more important and crucial to the constitutional framework. This is not a time for political cynicism or constitutional faithlessness. McConnell’s loyalty to Trump should not overwhelm his loyalty to the Constitution. If he fails in this, he is not only violating his Article I oath but his Article VI oath.

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Sen. Charles Schumer, the chamber's Democratic leader, is hitting the correct tone. He has called for the Senate to take its obligations seriously. He has called for the Senate to subpoena the documents Trump is hiding. He wants the trial to allow the time necessary for serious and sober evaluation of the facts. And key witnesses such as Mick Mulvaney and John Bolton should be called to testify.

The GOP line that the whole process is based on hearsay — not even accurate as an evidentiary matter — could be easily ameliorated by hearing from more people who have direct knowledge of Trump’s mendacity, abuse of power and attempts at cover-ups.

Short of declaring war, the Senate is about to conduct its gravest and most serious constitutional obligation — to exercise the “sole power to try” impeachments. All senators should take their obligation of faithful impartiality seriously, especially McConnell. History is watching, and it will be a harsh judge.

Kent Greenfield, a sixth-generation Kentuckian, is professor of law and Dean’s Distinguished Scholar at Boston College. This column originally appeared in the Louisville Courier Journal.