The letter Barack Obama wrote to Donald Trump, revealed seven months after Obama left office, focused on a central piece of advice - despite the difficulty of the political struggles and of the power battles, never lose sight of the importance of democratic institutions.
The handwritten note, folded in an envelope addressed to "Mr. President", starts with a word congratulation on a "remarkable run".
"Millions have put their expectations in you, and every one of us, paying little respect to party, should seek after extended flourishing and security amid your tenure".
Animosity has defined the pair's relationship for years - for instance, Mr Trump famously offered $US5 million ($6.25 million) to anyone who could produce Mr Obama's birth certificate, because he claimed Mr Obama was born in Kenya. Not everyone is so lucky.
His second reflection talks about "American leadership", and how it's indispensable for the world.
Remember America's role on the global stage: Obama called America's leadership in the world "indispensable" and reminded Trump that both through action and example, it's up to the US "to sustain the worldwide order that's expanded steadily since the end of the Cold War, and upon which our own wealth and safety depend".
When an Obama aide returned the call, one of Trump's staffers just said the president wanted to thank his predecessor and make sure he got the message.
Some of these maxims include equal protection and civil liberties, separation of powers, as well as the rule of law.
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Spend time with family: According to Obama, the key to work-life-balance for even world leaders centers on making time for what's important: family and friends. "But you know that when you get into recommending to spend more time with family, it becomes a formality".
Obama concluded the letter wishing Trump and wife, Melania, the "very best" on behalf of himself and wife, Michelle.
First, we've both been blessed, in different ways, with great good fortune. He signs, "Good luck and Godspeed, BO".
When Mr Trump opened the enveloped note on January 21, he reportedly attempted to call Mr Obama to express his gratitude, CNN reports.
The White House declined to comment, as did a spokesman for Mr Obama. 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".
Mr Obama even offers Mr Trump a lifeline in the note's closing. "And I think it's spoke to some concerns the majority of Americans had in the election", Tanden said. "It was long. It was complex".
Shortly after taking office, Trump praised the letter in an interview with ABC News.
Bush's father, George H.W. Bush, wrote Clinton back in 1992 that "your success now is our country's success", adding, "I am rooting hard for you".
Since reading the letter for the first time, Trump hasn't spoken or seen Obama.