According to The Verge
Twitter has placed a public interest notice on a tweet from President Trump for breaking the platform’s rules about the “glorification of violence.” However, Twitter has not chosen to remove the tweet from its platform entirely, because it believes it to be in the public interest. Twitter announced the notice in a tweet thread from its official comms account.
The notice means that the tweet is hidden from Trump’s timeline, but is accessible if you visit the tweet directly after clicking a “view” button. The reach of the tweet will also be limited as part of the process. Although users can still retweet it with a comment, they cannot reply to it, retweet it directly, or like it. Twitter also says that its notice means that the tweet won’t be algorithmically recommended on its platform.
Twitter seemed to be taking issue with Trump’s line “when the looting starts, the shooting starts.” Twitter referred to that quote’s historical connection to violence as reason for today’s action.
Trump is intentionally or inadvertently quoting former Miami Police Chief Walter Headley. In December 1967, months before riots broke out during the (Nixon) Republican National Convention, Headley said “when the looting starts, the shooting starts” at the announcement of a new “get tough” policy for policing black neighborhoods.