Taking to Twitter King called the US leader “a remarkable combination of unhinged and dumb as dirt.”
He added: “Time to start talking impeachment. Really. Enough is enough.”
King, who has been a consistent critic of the US President, spoke out after Mr Trump fired Mr Comey, who was leading an investigation into alleged links between his presidential campaign and Russia.
King’s tweet has been retweeted more than 29,000 times and liked almost 78,000 times. The author has previously criticised Mr Trump for his lack of transparency regarding his taxes.
“Come on, chickens**t, if you’re man enough to drop a mega-bomb on Afghanistan, you should be man enough to release your tax returns,” Mr King said.
King has also claimed that he believes Mr Trump resembles two characters from his books – Greg Stillson (The Dead Zone, 1979) and Big Jim Rennie (Under the Dome, 2009).
“In The Dead Zone, Greg Stillson is a door-to-door Bible salesman with a gift of gab, a ready wit and the common touch. He is laughed at when he runs for mayor in his small New England town, but he wins,” Mr King wrote.
He added: “Big Jim Rennie in Under The Dome is cut from the same cloth. He’s a car salesman (selling being a key requirement for the successful politician), who is the head selectman in the small town of Chester’s Mill, when a dome comes down and cuts the community off from the world.
“He’s a crook, a cozener and a sociopath, the worst possible choice in a time of crisis, but he’s got a folksy, straight-from-the-shoulder delivery that people relate to.
“The fact that he’s incompetent at best and downright malevolent at worst doesn’t matter.”