If someone is that corrupt or incompetent, they will get tossed...has happened, does happen, will continue to happen, regardless if they're on a probationary contract or a 5 year term (the longest contract term available). And unless the superintendent is grossly incompetent, it takes at least 2-3 years to see if their direction is working or not.

To answer your question, the 5th grade teacher can cause the most damage, as they are working directly with the students on a daily basis...especially if they continue to use unsuccessful strategies and policies that a new superintendent is changing.