Estimate the influence of the witches on Macbeth?

This is a good question. I think the witches have a lot of influence on Macbeth. Keep in mind that they can't make him do anything. Their suggestions drive Macbeth to go on his murderous rampage. Although a good soldier, Macbeth is insecure and riddled with doubt. He likes the idea of being King but is scared to play "foully" for it. Lady Macbeth seems to have more power over him, at least initially. Still, as the play goes on and Macbeth slips deeper and deeper into his own madness, the witches play a greater influence. They tell him what he wants to know, through their riddles, and that contributes to his final undoing.