With that said, I get the sense there is a large part of a story that is not being told here. Where was the manager? Has this employee had a history of maintaining appropriate professional boundaries with respect to communication? If Facebook doesn't have the appropriate paper trail, they could easily be sued for retaliation.
Possibly personal opinion here, but given the current charged (understatement) political environment and twitter's propensity for "scarlet lettering" people via mob harassment, I don't think this was borderline. This seems like a deliberate attempt to get a large group of people to harass a co-worker because of differing opinions about how and when to communicate political opinions.