>Not unless the government is the entity doing the banning (or collaborating with Twitter to ban accounts at its request).

But twitter is working with the government in hosting the tweets and thus assumes responsibility to provide a public square, in which case it cannot ban people.

Otherwise government should be banned from using twitter because by picking a private company to put government messages on, the government official (in this case Trump) is picking that company's existing policy (what ever it may be) as a means of banning people, which the government isn't allowed to do.