As President Joe Biden prepared to pass the baton to President-elect Donald Trump, he followed the tradition of leaving his successor a note.

While Biden confirmed he wrote Trump a letter, he did not disclose what his message said.

President Ronald Reagan started the ritual in 1989, according to The Washington Post, when he left a note for his former running mate, President George H.W. Bush.

He used light-hearted stationery that said, “Don’t let the turkeys get you down,” with a drawing of turkeys climbing on top of an elephant. Reagan wrote, “I treasure the memories we share and I wish you all the very best. You’ll be in my prayers. God bless you & Barbara. I’ll miss our Thursday lunches.”

Every president since has taken part in the tradition. But since Reagan’s letter to Bush, each handover has been from a Democrat to a Republican or vice versa.

Bush, who lost the 1992 election to Bill Clinton, said to the nation’s new leader, “Don’t let the critics discourage you or push you off course.”

“You will be our President when you read this note,” he wrote. “I wish you well. I wish your family well. Your success now is our country’s success. I am rooting hard for you. Good Luck.”

“I love that letter,” Clinton told ABC News in 2018. “I thought it was vintage George Bush. I thought he meant it, but I also thought he was trying to be a citizen in the highest sense of the word. It was profoundly moving to me personally.”

Clinton followed his predecessor’s tradition in 2001, when he said in a letter to President George W. Bush, “Today you embark on the greatest venture, with the greatest honor, that can come to an American citizen.”

“Like me, you are especially fortunate to lead our country in a time of profound and largely positive change, when old questions, not just about the role of government, but about the very nature of our nation, must be answered anew,” Clinton said. “You lead a proud, decent, good people. And from this day you are President of all of us. I salute you and wish you success and much happiness.”

“The burdens you now shoulder are great but often exaggerated. The sheer joy of doing what you believe is right is inexpressible,” he wrote. “My prayers are with you and your family. Godspeed.”

In 2009, George W. Bush wrote to President Barack Obama, “Congratulations on becoming our President. You have just begun a fantastic chapter in your life.”

“Very few have had the honor of knowing the responsibility you now feel. Very few know the excitement of the moment and the challenges you will face,” he said. “There will be trying moments. The critics will rage. Your ‘friends’ will disappoint you. 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. God bless you.”

When Obama handed off to Trump in 2017, he wrote to his successor, “Congratulations on a remarkable run. Millions have placed their hopes in you, and all of us, regardless of party, should hope for expanded prosperity and security during your tenure.”

“We’ve both been blessed, in different ways, with great good fortune,” Obama said, according to CNN. “Not everyone is so lucky. It’s up to us to do everything we can (to) build more ladders of success for every child and family that’s willing to work hard.”

Obama noted later in the letter, “We are just temporary occupants of this office. 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.”

He concluded by saying, “Michelle and I wish you and Melania the very best as you embark on this great adventure, and know that we stand ready to help in any ways which we can.”

Trump described Obama’s letter as “long,” “beautiful” and “so well-written, so thoughtful.”

“I called him and thanked him for the thought that was put into that letter,” Trump told ABC News “World News Tonight” anchor David Muir in 2017.

Then, in 2021, despite the contentious handover from Trump to Biden when Trump refused to admit he lost the 2020 election, Trump did follow tradition and leave Biden a note.

Biden described it as a “very generous letter,” according to Politico. The letter has never been released.

ABC News’ Justin Ryan Gomez contributed to this report.