Twitter briefly banned Donald Trump's campaign account from tweeting on Wednesday until it agreed to remove a video in which he made false claims about Covid-19.
In the most radical action against the President by any major social network so far, the company said on Wednesday that it had temporarily frozen @TeamTrump due to a breach of its coronavirus misinformation rules.
The offending tweet contained a video clip from a TV interview in which Mr Trump himself claimed that children are "almost immune" from Covid-19. In fact, research suggests that children can spread the virus as easily as adults, and some children have died from it.
Facebook also removed the video, the first time it has taken down any speech of Mr Trump's for coronavirus misinformation and potentially the first time it has ever ruled on the truth of Mr Trump's own words.
Mr Trump's campaign soon began tweeting again, and a spokesman for Twitter confirmed that the tweet had been removed on Wednesday night. Had the campaign refused, its ban could in theory have been indefinite.
Twitter said: "The @TeamTrump tweet is in violation of the Twitter rules on Covid-19 misinformation. The account owner will be required to remove the tweet before they can tweet again."
The president's account still has a tweet linking to the now-removed campaign message:
Both Facebook and Twitter have aggressively censored claims of fact about coronavirus that conflict with the advice of health authorities such as the World Health Organization (WHO). The companies argue that such claims must be treated strictly because they pose a clear risk of real-world harm.
The policy has won grudging praise from critics who have long urged both services to take a firmer stance on fake news, but also increased the pressure to tighten their rules in other areas.
Facebook's chief executive, Mark Zuckerberg, has repeatedly said that he does not want Facebook to be the "arbiter of truth". In the past, he has argued that removing coronavirus misinformation does not break this vow because it is public health officials, and not Facebook, deciding what is false.
Each company's action is significant in different ways. Facebook has long been accused of treating the President with kid gloves, causing more than 1,000 US advertisers to date to boycott its service.
Facebook has previously removed some of Mr Trump's adverts, and placed information labels on his posts about US election rules. However, this appears to be the first time that it ruled against the truth of Mr Trump's own words.
Twitter, meanwhile, has long been associated with the President, with years of fiery tweets from his personal account serving as a springboard for his fateful 2016 Republican primary campaign.