James Clapper explains the contents of the 'beautiful letter' he sent to Trump

The day after James Clapper, the former director of national intelligence, questioned President Donald Trump's fitness for office, the president shot back at the veteran intelligence leader, calling him a liar and implying he's a hypocrite.

"James Clapper, who famously got caught lying to Congress, is now an authority on Donald Trump," Trump tweeted on Thursday, referring to Clapper's 2013 testimony before Congress in which he denied that intelligence officials "wittingly" collected data on millions of Americans.

"Will he show you his beautiful letter to me?" Trump added.

Clapper told CNN in an interview on Thursday that the president was referring to a note he sent Trump the day after his election.

"The night before the election, we deployed two teams so that we would be ready to provide a PDB brief the next morning to whomever won," Clapper said, referring to the Presidential Daily Briefing. "I hand-wrote almost identical short notes to each of the two candidates to accompany the first brief as President-elect; only one actually got deployed - the one to him."

Both letters, only one of which was delivered, congratulated the candidates on their victories and affirmed the intelligence community's commitment to serving the White House.

"I went on to say that I hoped he would abide by the long-standing principle of the IC always telling 'truth to power,'" Clapper said, referring to the intelligence community.

But apparently Trump took the letter as a great compliment. Clapper said the president-elect thanked him three times for the note during Clapper's visit to Trump Tower for an intelligence briefing on January 6.

But five days later, the president lashed out at the intel community after CNN reported that then-FBI Director James Comey had briefed Trump on a salacious dossier compiled by a former British intelligence officer.

"Intelligence agencies should never have allowed this fake news to 'leak' into the public," Trump tweeted. "One last shot at me. Are we living in Nazi Germany?"