Indeed he is in great fear, not knowing what mighty one may suddenly appear, wielding the Ring, and assailing him with war, seeking to cast him down and take his place. That we should wish to cast him down and have no one in his place is not a thought that occurs to his mind.
This is why purely evil characters are much more dull than good ones. They are predictable. Good is never perfect, but the cackling evil villain can't imagine how to be good. They lack the necessary perspective.
