You're on a privately-owned site. The 1st Amendment limits the government, not the owners of privately-owned forums.
You need to go back to school.
He didn't "break in," he was an authorized user, so we can't get him for hacking.
It was political speech, so I don't think we can get him on obscenity.
JimRob has every right to kick him out - you're right. Freedom of speech guarantees no one a forum. But that's not what we're talking about here. We're talking about a criminal prosecution. I see that as tricky.