Even as a private citizen it is arguable that he has violated Twitter rules regarding violent threats, harassment and hateful conduct.
House of Cards creator and vocal opponent of Donald Trump Beau Willimon has suggested that the president’s Twitter account “facilitates national security threats” and must be taken down in accordance with the social network’s rules.
While you cannot prevent the President from saying reckless things elsewhere, @Twitter is not obligated to facilitate that here.
What the President tweets has real and significant impact on the business of governance, world affairs and national security.