For the first time, one of the President's tweets have been given a Twitter "fact-check" label, warning that this particular tweet was "unsubstantiated".
The tweet in question read: "There is NO WAY (ZERO!) that Mail-In Ballots will be anything less than substantially fraudulent."
There was no evidence posted to support the commander-in-chief's claim about mail-in ballots.
Twitter responded to the tweet with a fact-checking label, and posted a link which takes users to a page claiming that Mr Trump's claims were indeed "unsubstantiated".
Mr Trump responded today by warning the platform it could be "strongly regulated" or even "[closed] down".
He also claimed that Republicans felt "social media platforms totally silence Conservatives voices" and urged social media to "clean up [its] act, NOW!!!"
Finally, hours later, he promised "big action to follow" for the platform, who have recently announced changes to how they vet tweets posted by those with large numbers of followers. Mr Trump has more than 80 million.