The loophole that seems to be being exploited is that they’re allowed to redefine existing federal lands as military bases thus side stepping posse comitatis act. I don’t think they can just declare any land (E.G. state owned or privately owned land) part of a military base and there’s likely knock on effects from that as well. For instance I’d be surprised if there aren’t various laws about who and how you’re allowed to access “military bases” and therefore they can’t just slap one in the middle of a campus at least not without opening a giant can of worms.