The letter, while not the first one left from outgoing president to successor, was seen by many as a profound reminder of political bipartisanship, and since then the gesture has embedded itself in presidential tradition.
As 2021’s Inauguration Day nears, the nation continues to face unprecedented political instability, with President Donald Trump refusing to concede amid continued baseless attacks on the US electoral system.
And with less than a month until the end of Mr Trump’s presidency, it appears increasingly unlikely the president will be willing to extend a similar olive branch to President-elect Joe Biden, amid reports he may not even attend the Inauguration Day itself.
In turn, there seems to be no better time to reflect back on the inspiring final messages from presidents gone by to the successors that replaced them.
In 2016 Barack Obama used his letter to Donald Trump in part to reflect on the president's obligation to uphold democracy, a sentiment that now seems even more startlingly relevant in 2020.
“We are just temporary occupants of this office,” Mr Obama wrote. “That makes us guardians of those democratic institutions and traditions – like rule of law, separation of powers, equal protection and civil liberties – that our forebears fought and bled for.
“Regardless of the push and pull of daily politics, it's up to us to leave those instruments of our democracy at least as strong as we found them.”
Despite the lukewarm relationship between the outgoing and the incoming president, Mr Obama congratulated Mr Trump on a “remarkable run” and offered to “stand ready to help in any ways which we can”.
At the time, Mr Trump called the letter from his predecessor “thoughtful” and “beautiful”.
George W Bush
On 20 January 2009, George W Bush left Mr Obama a candid note of encouragement and congratulations, saying the incoming president had “just begun a fantastic chapter in your life”.
“There will be trying moments. The critics will rage,” his letter read.“But, you will have an Almighty God to comfort you, a family who loves you, and a country that is pulling for you, including me."
“No matter what comes, you will be inspired by the character and compassion of the people you now lead.”
Writing to incoming president George W Bush, from what he described as a “time of profound and largely positive change”, Bill Clinton spoke in his Inauguration letter of the joy of being president.
“When old questions, not just about the role of government, but about the very nature of our nation, must be answered anew,” the letter read.
“The burdens you now shoulder are great but often exaggerated. The sheer joy of doing what you believe is right is inexpressible.”
George H W Bush
Drawing on a gesture penned to him by predecessor Ronald Reagan, the significance of the message left by Mr H W Bush to Mr Clinton is often summed up in one singular quote:
“Your success now is our country's success. I am rooting hard for you.”
Mr Bush also wrote of the “sense of wonder and respect” that he felt walking into the Oval Office adding: “I know you will feel that, too.”
In an opinion column for The Washington Post in 2018 Mr Clinton said the letter revealed the 41st president as an “honourable, gracious and decent man who believed in the United States, our Constitution, our institutions and our shared future”.
Presidential historian Mark K Updegrove told The New York Times in 2018 that the Inauguration letter tradition as we know it was born from the humorous note Ronald Reagan left “to welcome an old friend to the White House”.
Mr Reagan used stationery with the letterhead “Don’t let the turkeys get you down” and a cartoon drawing of turkeys sitting on an elephant, the symbol of the Republican Party.
“You’ll have moments when you want to use this particular stationery. Well, go to it,” the letter read.
“God bless you and Barbara. I’ll miss our Thursday lunches.”
Joe Biden will take the oath of office and be sworn in as the 46th president of the United States on 20 January 2021.