On the day that congress counted the votes that confirmed Joe Biden as the winner of November's election, Trump spoke at a nearby rally insisting that the election had been "stolen" as a result of widespread voter fraud.
A large group of his supporters then stormed the Capitol Building, leaving five people dead in what turned out to be one of the darkest days in US history.
Schwarzenegger - former Republican governor of California - has previously been criticised by Trump after the actor replaced him on The Celebrity Apprentice but now Schwarzenegger has delivered a withering assessment of his old adversary's time in office.
In a lengthy video, Austria-born Schwarzenegger talks movingly about the effects that Nazi persecution in the Second World War had upon his family as he grew up - arguing that it came from the same sort of lies that Trump has been accused of perpetuating.
"President Trump is a failed leader," he said. "He will go down in history as the worst president ever.
"The good thing is he soon will be as irrelevant as an old tweet."
Watch Schwarzenegger's video, which also features his sword from Conan The Barbarian, below: