[WASHINGTON] What words of wisdom does the leader of the free world have for the man replacing him?

Letters that US presidents Bill Clinton and George W Bush wrote on their last day in office touch on the unique burden of the role - but also the joy that comes from serving in the highest office.

"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," Mr Clinton wrote to Mr Bush on Jan 20, 2001, according to a copy of the handwritten letter that Mr Bush's presidential library released to US media on Thursday.

"The burdens you now shoulder are great but often exaggerated. The sheer joy of doing what you believe is right is inexpressible," he wrote, adding that "from this day you are President of all of us".

"I salute you and wish you success and much happiness."

Exactly eight years later, Mr Bush penned a note to Barack Obama, telling him that "very few have had the honour of knowing the responsibility you now feel".

"Very few know the excitement of the moment and the challenges you will face," Mr Bush wrote in the letter.

"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."

Mr Obama is expected to carry on the tradition with a note to Donald Trump, who will be inaugurated just before noon on Friday.

AFP