CNN published a copy of the Inauguration Day letter former President Obama penned for President Trump.

In the days before Donald Trump's presidency, there were some interactions between the incoming and outgoing leaders.

CNN has obtained a copy of the Inauguration Day letter that former President Obama wrote to Trump.
Besides congratulating him on a "remarkable run," Obama offered "a few reflections" while mentioning "there's no clear blueprint for success."
"American leadership in this world really is indispensable," the former president wrote, in part. "It's up to us, through action and example, to sustain the international order that's expanded steadily since the end of the Cold War, and upon which our own wealth and safety depend."
Obama then went on to note that as "guardians" of the nation's democratic principles, it's up to the presidents to leave such "institutions and traditions -- like rule of law, separation of powers, equal protection and civil liberties" as strong as they were before the presidency.
In the end, Obama offered help to Trump whenever needed.
However, based on the apparent state of the relationship between the two, Trump doesn't seem to have sought much assistance from the former president. 
In fact, Trump has repeatedly criticized Obama on trade deals, regulations, treaties, and other issues.
The president also accused him of wiretapping Trump Tower when he tweeted on March 4, "Terrible! Just found out that Obama had my 'wires tapped' in Trump Tower just before the victory. Nothing found. This is McCarthyism!"
In a follow up tweet, Trump said, "How low has President Obama gone to tapp my phones during the very sacred election process. This is Nixon/Watergate. Bad (or sick) guy!"
Obama's spokesperson has denied any such activity and the Department of Justice also recently confirmed in a court ruling that there's no evidence of wiretapping.