Growing up in Memphis TN, I've heard "fair to middlin" all my life with exactly the same meaning. I suppose it came from Yorkshire. The only other use of "middling" that I've heard is a reference to a medium grade of some commodity, a grain or cotton for example.
Sorry to hear you are in the position that you feel you need to change jobs, but I do know that happens. Caring for the welfare of others is not a liberal or conservative trait. It's what good people do and there's no way politics can possibly improve that. There are actually a few politicians who care for people.
Best wishes to you.