Consider, it like this. If Trump had a group of friends who he likes to discuss country's policy with. Is it legally binding that, he has to inculde everyone in that group and cannot ban enyone from his friend club? Consider this friend club to be his twitter followers.
P.S. I am not a republican or even an American. I am just trying to create a constructive dialogue about the ruling and what laws come to play to enforce it.
If he does so on a public forum, then he is not allowed to blacklist people from hearing/seeing it. He has the @POTUS account. If he's concerned about his public vs private privileges, he may wish to consider moving his government related tweets to the @POTUS account. At that point, he can tweet support for Tomi Laren (sp?) to his heart's content from his personal account. When he's discussing world stage stuff, though, that should stick to the POTUS account. That's all.