Istari and their staves

[Alcuin]

If a wizard’s staff from Aman was a reminder that he also came from Aman, then Gandalf’s breaking Saruman’s staff suddenly makes sense: his connection to home was broken. He’d been offered a chance to repent and be redeemed, but he refused. Saruman himself broke his real connection to Valinor; Gandalf’s breaking his staff only made him aware of what he had done. That would explain how Saruman might still trap a Nazgûl at Orthanc, how he could cozen Treebeard despite all he’d done to the ents and the fact that Treebeard actually understood his purposes, but without that connection back to Valinor, he was increasingly unfocused. When Gandalf’s body was killed, his spirit wandered but remained intact; when Saruman’s body was killed, his spirit was dissipated.

It also throws light on how Radagast failed in his mission. Radagast never became evil: Gandalf calls him “the honest Radagast”, and it was through Radagast’s interventions that Gwaihir rescued Gandalf from Orthanc. But Radagast “became enamored of the many beasts and birds that dwelt in Middle-earth, and forsook Elves and Men”. (Unfinished Tales, “Istari”) Gandalf’s description at the Council of Elrond of his meeting with him portrays Radagast as frightened and unfocused, as if he had forgotten his connection to Valinor and so lost his connection to his mission in Middle-earth.