The letter criticises Trump’s behaviour, calling the president a “circus orangutan” and highlighting a range of his recent controversies.
“Dear f****** luantic,” it starts. “At your recent press conference - more a word salad that had a stroke and fell down the stairs, you were CLEARLY so out of your depth you needed scuba gear.
“Within minutes of going off air your minions were backpedalling faster than Cirque du Soleil acrobats."
The letter highlights a range of controversies, such as when Trump called Kim Jon Un "short and fat" in 2017.
“You attempted — with evident f****** glee — to get 24 million people thrown off their health insurance,” it continues.
“You gave billions away to corporations and the already wealthy while simultaneously telling struggling poor people that you were doing exactly the opposite.”
Tommy Lee shared the post on his account, receiving thousands of retweets and likes, while a second posting of it, by user @MysterySolvent, also went viral.
Confusingly, Lee attributed the letter to someone named Craig Alan Wilkins, but US comedian Sarah Silverman cleared up the mystery when she retweeted the latter post, writing: “THIS IS F****** BRILLIANT **NOT WRITTEN BY Tommy Lee but @AJPennyfarthing”.
A version of the letter was originally shared on The Daily Kos by Aldous J Pennyfarthing in December 2017, following Trump’s interview with the New York Times.
On Twitter, Pennyfarthing welcomed his new followers, writing: “Yes, I'm the original author of the ‘Dear F****** Lunatic’ letter. Not Tommy Lee. I simply don't measure up to Tommy Lee.
"And here's the book of the same name. Buy it, read it, enjoy the japery.”
The book features “101 obscenely rude letters to Donald Trump”and was written by Pennyfarthing.