There are literally thousands of handwritten letters, many of them hundreds of years old, many penned by towering American figures, housed at the Massachusetts historical society. But few detail as auspicious a moment in American history as the one shown to me by digital archivist Neal Millikan.

It was written by John Adams to his wife Abigail in 1797, the day after the first peaceful transfer of power in American history, when Adams took office as our second President. 

The letter reads, in part:

In the chamber of the House of Representatives was a multitude as great as the space could contain, and I believe scarcely a dry eye but Washington’s. The site of the sun setting full orbit and another rising, though less splendid was a novelty. 

I had not slept well the night before and did not sleep well the night after. I was unwell and did not know if I should go through it or not. I did however. CJ Ellsworth administrated the oath and with great energy. 

The oath that Adams took that day is the same one Donald Trump takes today; the same one taken by every man who has ever risen to the office of the Presidency:

I do solemnly swear (or affirm) that I will faithfully execute the Office of President of the United States, and will to the best of my Ability, preserve, protect and defend the Constitution of the United States. 

That 35-word sequence is as old as our republic. And while our founding document requires oaths on several occasions, this is the only one the framers actually wrote out.

"The very first thing the president has to do is take that oath," said Michael Gerhardt, the Constitutional scholar-in-residence at the National Constitution Center in Philadelphia. "That tells us how important that is. It's the primary thing that really anchors his presidency."

Gerhardt said that the framers were not only seeking to empower the President, but also to limit that power. 

"They wanted to make sure that a President who would be a powerful official was not gonna be unbound," he said. "Beginning with the oath was the framers way of saying that 'we’re even gonna tell you, the President, what words you have to say to remind you that you serve the Constitution, and you serve the American people.'"

And it took some work for them to get there. At the Massachusetts Historical Society, librarian Peter Drummy shows me an early working draft of the Constitution that belonged to Massachusetts delegate to the Constitutional Convention Elbridge Gerry.

"[You can see] the wide margins full of manuscript notes that show the evolution of this text. This is history in real time," explained Drummy.

In this version, the oath is missing some key components, ending simply "...that I will faithfully execute the office of President of the United States of America." There is nothing about preserving, protecting or defending the Constitution. That came later, courtesy of an amendment proposed by Virginia delegates James Madison and George Mason.

"It was state by state, each having a single vote," said Drummy. "It passes by a majority, but this [was] not a unanimous change," said Drummy, noting that Massachusetts abstained from voting on the matter.

The oath is all the Constitution calls for on inauguration day. Everything else – from the address to the parades, the Chief Justice swearing the president in to the hand on the bible – are merely traditions. Also a tradition: the words that most presidents have chosen to add to the end of the oath: "So help me God."

Much will be made in the coming months about whether this new president is succeeding. Well, a good starting point might be to measure him against the venerable oath – a clear, simple description of the job written by the very men who invented it. And hey –  at 35 brief words –  it’s almost short enough to tweet.