Yes. If taxpayers are funding the mall space, they are entitled to assemble there. Any violation of that is a First Amendment case. It's why government doesn't

Yes. If taxpayers are funding the mall space, they are entitled to assemble there. Any violation of that is a First Amendment case. It's why government doesn't set up in malls, the malls won't let them. But a mall isn't the best analogy for Twitter because a Twtitterfight doesn't interfere with the rest of Twitter at all. The better analogy is a (soundproofed) hotel where your key granted you access to every room but the owner of the room can choose to deny you access. If the government (ie taxpayers) owns the room, they can't deny you access when conducting official business.