Gandalf's Staff

[Kuruharan]

Everything Gandalf did on that Bridge was just to scare ol' Roggie off. He could fight with it, yes, but he would lose time that he didn't have. But when the Balrog insisted on crossing the Bridge, he had to make sure it didn't reach the other end; ergo, the Bridge-breaking.

I'm not so sure that Gandalf expected to scare the Balrog off. The Balrog may have been mighty curious about this odd critter in front of him, a being which he knew to be Ainu (which the Balrog would probably have found odd enough) but not "dressed" as one. Uncertainty, but not necessarily fear, could possibly have been his dominant feeling.

I think Gandalf planned to break the bridge from the beginning. What better way to cut off pursuit?