Tenure isn't what you think it is. Tenure isn't necessarily supposed to be related to full-time status
Tenure isn't some magic "I can't be fired" button. It IS a "I am no longer an at will employee button". Once someone has tenure, you must have a documented reason to fire them. And those reasons are delineated up front.
People are upset that you are teaching evolution--not fireable. Teaching creationism in a science class--likely fireable(but unlikely to occur for various reasons). Too expensive a salary--not fireable. Dating a student--fireable even if you are both of age and consenting. Plagiarism or academic misconduct--fireable even if it wouldn't be so in private enterprise.
The problem is that school administrators tend to be very political--they are always working on getting their next job/promotion and need approval from their current/future teachers, current/future board, and current/future community. This interacts to form a feedback loop.
If an administrator gets a reputation for firing people, he's not going to get approval from the new teachers. Firing people costs money, so the next board is going to be suspicious. The new community may be staring at the fact that the old community rallied behind a teacher that the administrator tried to fire.
So, as an administrator, your best political bet is to shunt aside someone quietly rather than documenting and firing them.
If course, this assumes that the teacher actually needed to be fired. Administrators (especially in small schools) are notorious for playing petty political games of the "Do what I want or I'll give you the shitty class" kind. Older teachers tend to have zero tolerance for that kind of crap and, in small communities, may be able to zap the administrator for it and incur their wrath.
The thing you have to keep in mind is that the political situations in a large university, a small college, a large high school (like New York City), and a small high school (like rural New York) are VASTLY different and tenure serves slightly different purposes in each.