His opinion should not enter the classroom. If he cannot, or will not, leave his opinions at the schoolhouse door, he should be fired. No question about it.
The "teachers" who insist on bringing their political beliefs into the classrooms of our schools, are nothing more than incompetent at their jobs. They have still not learned what their jobs are, to teach whatever subject they are assigned. Let them get real jobs in the real world and see how they do. Not well, I would bet.