Tolkien Forums

Thew Witchking is not nearly as powerful as Gandalf. Although the Witchking has much power bestowed to him by Sauron and he gained power when he had one of the Rings of Power Gandalf is a Maiar spirit, an Angelic being who came before Ea. Although he was limited as to what power he could use the Witchking is unlikely able to break Gandalf's staff. That was just done in the film for effect.

For example in the book we see that Gandalf is able to hold off alot of Nazgul including the WK on top of Weathertop and then he was Gandalf the Grey, not Gandalf the White. Although I wouldn't say its immpossible for the WK to break Gandalf's staff at the Time of the battle of Pellenor, becuase we don't truly know how much power Sauron put into him between Weathertop and then, I would say its very unlikely.