The actor sat down for an interview to promote his new film "The Call of the Wild", about a man who, along with his newfound canine companion, embarks on a mission to find his place in the world, when the subject of the 45th POTUS came up in the conversation.
Jimmy presented the star with a poster for the flick, mocked-up with fake reviews from the President, which were inspired by Trump's famous insistence that his phone call with Ukrainian President Volodymyr Zelensky, which was at the centre of the recent impeachment inquiry, was "perfect".
"Have you seen the reviews?" Kimmel asked before reading out the fake reviews. "'That call was perfect - Donald J. Trump'...'This was a perfect call'."
"'It was a great call. Not just a good call, it was a perfect call.' The reviews are really pouring in," he laughed.
Harrison burst out laughing before adding: "That's the first thing that son of a b**ch has done for me... ever!".
And when Jimmy mentioned his next guest 'Science Bob' Pflugfelder, the "Blade Runner 2049" star joked: "We don't believe in science any more... Nobody here believes in science any more?".
The actor has previously spoken out against the Trump administration's attitude to environmental issues and apparent denial of climate change.
"The Call of the Wild" hits cinemas February 14.