they tend to move someone to an untenable situation (or pass them on to another area/school to be their problem) in hopes the person leaves voluntarily (e.g. strip their coaching position, move a HS teacher to elem, etc.). Or they simply don't renew their contract the following year, as "tenure" here and at the K-12 level is nothing like college "tenure".

Inability to fire poor teachers (or even poorly behaving teachers) has more to do with avoiding the cost of a wrongful termination suit, than any power the union has (which isn't much for the VA teachers union).