I too work in a politically charged environment. Ady's right about letting it swirl around you. I like the Kenny Rogers song and think of it often when in situations where the politics are sucking the oxygen out of the room. You gotta know when to hold 'em, know when to fold 'em, know when to walk away, and know when to run. Add into that the serenity prayer: the courage to change what I can, and the wisdom to know the difference.
To me, its all about mind-set. I am unflappable. I have a great poker face. I also know my own power, and you do not need to engage with your superintendent and your supervisor. That really is an HR issue; one that is very delicately played. I am surprised you are even being asked to meet again.
Don't ever hesitate to use the words "hostile work environment". HR folks get really nervous with that statement.
Find out what your rights are. Instead of fretting (and I understand why you are feeling the way you feel, that is not to be dismissive) go find out what you can do here. Can you file a complaint? Can you request a change in positions? A transfer to another school within the district?
And keep swirling around your supervisor. Like water in a stream full of rocks, swirl around the barriers in your way to keep doing a good job for the ones that really matter - the kids.